Fast idle conundrum
Discussion
My car has just developed a new habit of idling at around 1800-2000 rpm.
This started recently, as we now have temps above 25 deg (if that is a factor) and usually starts to happen after about 10 minutes of driving. I am assuming that engine bay temperatures may have something to do with it.
So after another 10 minutes of driving with comedy idling at lights, I pull up, open the bonnet and cannot see any hoses having come off from anywhere. So this morning, I pulled out the stepper motor, gave it a good clean (second time within 2 months) and starting from cold, the idle is all perfectly coming down as it should, and then after 10 minutes, it goes back up to 1800 - 2000 rpm.
So to check the stepper motor, next time I start it from cold, and as soon as it is idling around 1000 rpm (after the initial spike on startup) I pull out the stepper motor plug and the car keeps the 1000 rpm for about 10 minutes and I pat myself on the back in that I have diagnosed a faulty stepper. After about 10 minutes of driving, again, the revs slowly start climbing again and we are back at boy racer sounds at the lights again.
So it is not the stepper I say, so I get home, car is idling at 1800 rpm, I turn off the engine, to reset the stepper, plug the stepper plug back in and start it again, and the car is idling on my drive at 950 rpm again.
Honestly, I am at a loss as to where to look, as I would have thought that if there was a leak, then putting the stepper back in on an engine that is still hot and has just been stopped and restarted should not make a difference. A short time ago, I had an issue of the top hose coming off from the firetrap, and I have now secured that, but I don't know if this is a factor, but when I checked the engine bay before I put the stepper back on, that top hose was quite hard, ie I couldn't squash it as easily as I could when it is cold.
The small hose going from the plenum to the stepper housing, when squeezed, brings the idle down to the normal level, so that area is working too, isn't it? Can't hear any hissing anywhere, but then there is a lot of noise in the engine bay without a stethoscope I wouldn't know, but then, why would the stepper make a difference when I put it back on, but previously it could not do anything when connected?
This started recently, as we now have temps above 25 deg (if that is a factor) and usually starts to happen after about 10 minutes of driving. I am assuming that engine bay temperatures may have something to do with it.
So after another 10 minutes of driving with comedy idling at lights, I pull up, open the bonnet and cannot see any hoses having come off from anywhere. So this morning, I pulled out the stepper motor, gave it a good clean (second time within 2 months) and starting from cold, the idle is all perfectly coming down as it should, and then after 10 minutes, it goes back up to 1800 - 2000 rpm.
So to check the stepper motor, next time I start it from cold, and as soon as it is idling around 1000 rpm (after the initial spike on startup) I pull out the stepper motor plug and the car keeps the 1000 rpm for about 10 minutes and I pat myself on the back in that I have diagnosed a faulty stepper. After about 10 minutes of driving, again, the revs slowly start climbing again and we are back at boy racer sounds at the lights again.
So it is not the stepper I say, so I get home, car is idling at 1800 rpm, I turn off the engine, to reset the stepper, plug the stepper plug back in and start it again, and the car is idling on my drive at 950 rpm again.
Honestly, I am at a loss as to where to look, as I would have thought that if there was a leak, then putting the stepper back in on an engine that is still hot and has just been stopped and restarted should not make a difference. A short time ago, I had an issue of the top hose coming off from the firetrap, and I have now secured that, but I don't know if this is a factor, but when I checked the engine bay before I put the stepper back on, that top hose was quite hard, ie I couldn't squash it as easily as I could when it is cold.
The small hose going from the plenum to the stepper housing, when squeezed, brings the idle down to the normal level, so that area is working too, isn't it? Can't hear any hissing anywhere, but then there is a lot of noise in the engine bay without a stethoscope I wouldn't know, but then, why would the stepper make a difference when I put it back on, but previously it could not do anything when connected?
jazzdude said:
My car has just developed a new habit of idling at around 1800-2000 rpm.
This started recently, as we now have temps above 25 deg (if that is a factor) and usually starts to happen after about 10 minutes of driving. I am assuming that engine bay temperatures may have something to do with it.
So after another 10 minutes of driving with comedy idling at lights, I pull up, open the bonnet and cannot see any hoses having come off from anywhere. So this morning, I pulled out the stepper motor, gave it a good clean (second time within 2 months) and starting from cold, the idle is all perfectly coming down as it should, and then after 10 minutes, it goes back up to 1800 - 2000 rpm.
So to check the stepper motor, next time I start it from cold, and as soon as it is idling around 1000 rpm (after the initial spike on startup) I pull out the stepper motor plug and the car keeps the 1000 rpm for about 10 minutes and I pat myself on the back in that I have diagnosed a faulty stepper. After about 10 minutes of driving, again, the revs slowly start climbing again and we are back at boy racer sounds at the lights again.
So it is not the stepper I say, so I get home, car is idling at 1800 rpm, I turn off the engine, to reset the stepper, plug the stepper plug back in and start it again, and the car is idling on my drive at 950 rpm again.
Honestly, I am at a loss as to where to look, as I would have thought that if there was a leak, then putting the stepper back in on an engine that is still hot and has just been stopped and restarted should not make a difference.
I think your test method is slightly flawed here. When you shut off the engine, the ECU withdraws the stepper completely, into the fully open position, ready for next engine start. This is why the revs spike when you start the engine in the first place. On a cold engine, immediately after a start, the stepper will be held open somewhat to keep the engine at the 1000ish rpm you saw. If you disconnect the stepper shortly after starting then you are locking it in a cold started open position. This started recently, as we now have temps above 25 deg (if that is a factor) and usually starts to happen after about 10 minutes of driving. I am assuming that engine bay temperatures may have something to do with it.
So after another 10 minutes of driving with comedy idling at lights, I pull up, open the bonnet and cannot see any hoses having come off from anywhere. So this morning, I pulled out the stepper motor, gave it a good clean (second time within 2 months) and starting from cold, the idle is all perfectly coming down as it should, and then after 10 minutes, it goes back up to 1800 - 2000 rpm.
So to check the stepper motor, next time I start it from cold, and as soon as it is idling around 1000 rpm (after the initial spike on startup) I pull out the stepper motor plug and the car keeps the 1000 rpm for about 10 minutes and I pat myself on the back in that I have diagnosed a faulty stepper. After about 10 minutes of driving, again, the revs slowly start climbing again and we are back at boy racer sounds at the lights again.
So it is not the stepper I say, so I get home, car is idling at 1800 rpm, I turn off the engine, to reset the stepper, plug the stepper plug back in and start it again, and the car is idling on my drive at 950 rpm again.
Honestly, I am at a loss as to where to look, as I would have thought that if there was a leak, then putting the stepper back in on an engine that is still hot and has just been stopped and restarted should not make a difference.
When the engine gets hot, the stepper should be pretty much closed (probably not completely closed) for the target rpm, but since you've locked it in a cold started 1000rpm position, then you're going to get a high idle when it is up to temperature. This is why plugging it back in and restarting the engine brings the revs back down again; because the stepper can now be closed to the correct position for the now fully warmed up engine.
jazzdude said:
A short time ago, I had an issue of the top hose coming off from the firetrap, and I have now secured that, but I don't know if this is a factor, but when I checked the engine bay before I put the stepper back on, that top hose was quite hard, ie I couldn't squash it as easily as I could when it is cold.
The small hose going from the plenum to the stepper housing, when squeezed, brings the idle down to the normal level, so that area is working too, isn't it? Can't hear any hissing anywhere, but then there is a lot of noise in the engine bay without a stethoscope I wouldn't know, but then, why would the stepper make a difference when I put it back on, but previously it could not do anything when connected?
Your symptoms sound like an air leak to me, although there are no doubt other possible explanations, but it might just be that you need to readjust the base idle. It is normally set so that with the bypass hose fully clamped you get about 600rpm so if when clamping it you get a 'normal level' then either the base idle is not set correctly or you have an air leak somewhere. You need to rule out an air leak first though otherwise setting the base idle won't help or will just mask the problem.The small hose going from the plenum to the stepper housing, when squeezed, brings the idle down to the normal level, so that area is working too, isn't it? Can't hear any hissing anywhere, but then there is a lot of noise in the engine bay without a stethoscope I wouldn't know, but then, why would the stepper make a difference when I put it back on, but previously it could not do anything when connected?
The thing about air leaks is they can come and go according to engine temperatures or movement in hoses while running etc, so an unpredictable behaviour is not out of the ordinary.
When I took the stepper block off, the engine was already warm so I don't think the rise in the idle speed was to do with cold starting.
As I said the idle held more or less constantly for about 10 mins of town stop start driving. It started climbing again more or less the same way as when the stepper was connected once the temps got to where the fans would kick in.
I set the base idle a couple of months ago after changing the dizzy and resetting the timing. I had used the bung method rather than clamping it and the car was running perfectly for a while. This whole high idling started after I took off all the pipework in front of the engine to tidy up the wiring.
As all the hoses went back to their original positions and are all clamped with jubilee clips I cant for the life of me imagine where a leak could now be. I wrote on a previous thread about the top hose popping off the flame trap and I have fixed that now.
I'm not sure what the correct sequence would be in isolating one hose at a time until I find the leak or how to go about going over everything methodically either.
I read that spraying carb cleaner or something like that around could the top of the engine could provoke a spike in revs but the thought of a flammable material being sprayed around hot manifolds doesn't seem like a bright idea.
Could something like a loose plenum bolt cause this as I haven't checked those yet. What else would open up a leak only when the engine bay gets to fan temp? There were a couple of steam squirt coming out of the expansion tank cap when I got home, opened the bonnet and reconnected the stepper if that makes any difference.
The only other thing I changed recently was the AFM, I replaced the one it had with a 'good' used one that I bought from Jules a couple of months ago.
As I said the idle held more or less constantly for about 10 mins of town stop start driving. It started climbing again more or less the same way as when the stepper was connected once the temps got to where the fans would kick in.
I set the base idle a couple of months ago after changing the dizzy and resetting the timing. I had used the bung method rather than clamping it and the car was running perfectly for a while. This whole high idling started after I took off all the pipework in front of the engine to tidy up the wiring.
As all the hoses went back to their original positions and are all clamped with jubilee clips I cant for the life of me imagine where a leak could now be. I wrote on a previous thread about the top hose popping off the flame trap and I have fixed that now.
I'm not sure what the correct sequence would be in isolating one hose at a time until I find the leak or how to go about going over everything methodically either.
I read that spraying carb cleaner or something like that around could the top of the engine could provoke a spike in revs but the thought of a flammable material being sprayed around hot manifolds doesn't seem like a bright idea.
Could something like a loose plenum bolt cause this as I haven't checked those yet. What else would open up a leak only when the engine bay gets to fan temp? There were a couple of steam squirt coming out of the expansion tank cap when I got home, opened the bonnet and reconnected the stepper if that makes any difference.
The only other thing I changed recently was the AFM, I replaced the one it had with a 'good' used one that I bought from Jules a couple of months ago.
jazzdude said:
When I took the stepper block off, the engine was already warm so I don't think the rise in the idle speed was to do with cold starting.
I was replying on the basis of this:jazzdude said:
So to check the stepper motor, next time I start it from cold, and as soon as it is idling around 1000 rpm (after the initial spike on startup) I pull out the stepper motor plug
Which does suggest you did it straight away without letting it warm up. Perhaps that wasn't what you intended.jazzdude said:
As I said the idle held more or less constantly for about 10 mins of town stop start driving. It started climbing again more or less the same way as when the stepper was connected once the temps got to where the fans would kick in.
I set the base idle a couple of months ago after changing the dizzy and resetting the timing. I had used the bung method rather than clamping it and the car was running perfectly for a while. This whole high idling started after I took off all the pipework in front of the engine to tidy up the wiring.
How loose was the idle screw when you adjusted it? Worth checking it is not loose as if so it may vibrate into another orientation.I set the base idle a couple of months ago after changing the dizzy and resetting the timing. I had used the bung method rather than clamping it and the car was running perfectly for a while. This whole high idling started after I took off all the pipework in front of the engine to tidy up the wiring.
jazzdude said:
As all the hoses went back to their original positions and are all clamped with jubilee clips I cant for the life of me imagine where a leak could now be. I wrote on a previous thread about the top hose popping off the flame trap and I have fixed that now.
Hoses are not the only source of leaks. Manifold gasket is another for example. I'm obviously by no means certain it is a leak, but I guess it needs to be ruled out. Google for techniques for finding leaks - e.g. spraying easy start around everything (actually I see you mentioned this already) - choose a method you're comfortable with from a safety perspective.jazzdude said:
I'm not sure what the correct sequence would be in isolating one hose at a time until I find the leak or how to go about going over everything methodically either.
I read that spraying carb cleaner or something like that around could the top of the engine could provoke a spike in revs but the thought of a flammable material being sprayed around hot manifolds doesn't seem like a bright idea.
Could something like a loose plenum bolt cause this as I haven't checked those yet. What else would open up a leak only when the engine bay gets to fan temp? There were a couple of steam squirt coming out of the expansion tank cap when I got home, opened the bonnet and reconnected the stepper if that makes any difference.
There shouldn't be any steam coming out of the cap but that could just be a weak cap that needs replacing. Assuming you don't have any other engine issues of course.I read that spraying carb cleaner or something like that around could the top of the engine could provoke a spike in revs but the thought of a flammable material being sprayed around hot manifolds doesn't seem like a bright idea.
Could something like a loose plenum bolt cause this as I haven't checked those yet. What else would open up a leak only when the engine bay gets to fan temp? There were a couple of steam squirt coming out of the expansion tank cap when I got home, opened the bonnet and reconnected the stepper if that makes any difference.
jazzdude said:
The only other thing I changed recently was the AFM, I replaced the one it had with a 'good' used one that I bought from Jules a couple of months ago.
The AFM tends to affect the fuelling (makes it run rich often) but I guess that could start to make the engine revs rise depending on other conditions. You can check the AFM with bltzracing's info which no doubt you are already aware of.Unfortunately it's super difficult for anyone to debug this sort of issue remotely. You may just have to hand it over to someone else if you can't find it yourself.
There are some other symptoms here that are spiking my interest.
Just a thought...discuss.
Steve
- Steam from rad cap.... could be a duff cap or pressurized engine due to head gasket fail.
- Breather hose popping off the flame trap.... Could just be a slippery hose or crank case pressure again possibly from the head gasket. I think there was also mention of this hose being 'Hard' but soft when the engine was off/cold.
Just a thought...discuss.
Steve
So spent a couple of hours out there this morning.
Checked all the hoses, took them off, checked them for splits, cleaned them, added a little vaseline, and put it all back together.
I was under the dash getting the RG lead out to connect to pc and to my horror, found that the wires going into the connector which the white resistor is connected to (I also have a green resistor that I have experimented with, hence the block connector) was loose, probably out, so there is a chance the car was running on non-map mode, unless the wire popped out while I was under there opening the dash flap. Possible cause 1.
Once connected to RG and then getting the car running to the point the fans kicked in, I was then shocked to see the engine temp go up to 130 degrees without the fans coming on. So clicked on the fans overide switch and then the engine temp on RG started fluctuating between 35 degs and 130 degs. This was a brand new engine temp sender from TVR parts that I fitted a couple of months ago. Put the old one back on and now can see a steady reading so all is well there. So possible cause 2.
So letting it idle into the fans temp, the fans come on and I see the idle starting to climb again, I increased the throttle a little and revs then came back down, but settled on 1500 rpm again. This time though I could close the stepper in RG by 30 steps and the idle settled back to 975rpm.
Playing with RG and the stepper, there were definitely points where it seemed the stepper was not moving and the rpm stayed high, but then manually moving it, it then started working normally and you could see RG changing the percentages backwards and forwards a little. Possible cause 3, or a bit of all the above.
The fans stayed on for a while (not turning off in the 2-3 minutes it usually takes) so I am suspecting that there is air in the system or it needs a top up which I will do later, but the comment about the head gasket and pressure in the crank has concerned me, how do I check for this, as there are no signs of smoke or it burning any oil.
Now this would be interesting....
Checked all the hoses, took them off, checked them for splits, cleaned them, added a little vaseline, and put it all back together.
I was under the dash getting the RG lead out to connect to pc and to my horror, found that the wires going into the connector which the white resistor is connected to (I also have a green resistor that I have experimented with, hence the block connector) was loose, probably out, so there is a chance the car was running on non-map mode, unless the wire popped out while I was under there opening the dash flap. Possible cause 1.
Once connected to RG and then getting the car running to the point the fans kicked in, I was then shocked to see the engine temp go up to 130 degrees without the fans coming on. So clicked on the fans overide switch and then the engine temp on RG started fluctuating between 35 degs and 130 degs. This was a brand new engine temp sender from TVR parts that I fitted a couple of months ago. Put the old one back on and now can see a steady reading so all is well there. So possible cause 2.
So letting it idle into the fans temp, the fans come on and I see the idle starting to climb again, I increased the throttle a little and revs then came back down, but settled on 1500 rpm again. This time though I could close the stepper in RG by 30 steps and the idle settled back to 975rpm.
Playing with RG and the stepper, there were definitely points where it seemed the stepper was not moving and the rpm stayed high, but then manually moving it, it then started working normally and you could see RG changing the percentages backwards and forwards a little. Possible cause 3, or a bit of all the above.
The fans stayed on for a while (not turning off in the 2-3 minutes it usually takes) so I am suspecting that there is air in the system or it needs a top up which I will do later, but the comment about the head gasket and pressure in the crank has concerned me, how do I check for this, as there are no signs of smoke or it burning any oil.
Now this would be interesting....
Airlock in cooling system rather than a dodgy temp sensor would be my first thought.
Take expansion cap off and smell into the bottle. If exhaust gases are present you might be able to smell them. Very rough test but often gives clues regarding head gasket leaks.
Keep a close eye on your oil colour. If water is present you might get some mayo on the inside of your oil filler cap. Do the mayo test by not letting engine get fully upto temp or it might well burn off as you live in such a hot country.
Separately your stepper motor might be momentarily sticking once it’s hot as that’s how mine would play up. Once it’s even a few steps out of sync it will give odd idle until it’s switched off and hopefully gets pulled back to its zero position and you start again! It’s very fustrating.
Is heat effecting a bad connection in the starter circuit or a component is failing once warm. Volt meter and some tests maybe.
Good luck.
Take expansion cap off and smell into the bottle. If exhaust gases are present you might be able to smell them. Very rough test but often gives clues regarding head gasket leaks.
Keep a close eye on your oil colour. If water is present you might get some mayo on the inside of your oil filler cap. Do the mayo test by not letting engine get fully upto temp or it might well burn off as you live in such a hot country.
Separately your stepper motor might be momentarily sticking once it’s hot as that’s how mine would play up. Once it’s even a few steps out of sync it will give odd idle until it’s switched off and hopefully gets pulled back to its zero position and you start again! It’s very fustrating.
Is heat effecting a bad connection in the starter circuit or a component is failing once warm. Volt meter and some tests maybe.
Good luck.
Continued with my checks, following the odd behavior of the fans and temperature not dropping, I bled the system and topped it up.
Although their was a couple of inches of coolant in the expansion tank, the level swirl pot was about a quarter empty which concerns me.
All in all, after I had opened the bleed valve on the radiator the car needed about 2 litres of coolant to fill up the swirl pot until the fans came on, which is I think is unusual. During the last month of driving the temp guage in the car (on the Rover sender, not the TVR one) never went over 95, but I now think that the fans must have been on all the time as I saw earlier today.
During this, the idle was a steady 950 rpm and I took this opportunity afterwards to also check the base idle which needed a slight adjustment.
If the coolant was low could it be that these higher temperatures causing this erratic idling?
I also don't understand how it needed so much coolant, and why there was such a large air pocket in the swirl pot even though there was a couple of inches of coolant in the expansion tank.
Although their was a couple of inches of coolant in the expansion tank, the level swirl pot was about a quarter empty which concerns me.
All in all, after I had opened the bleed valve on the radiator the car needed about 2 litres of coolant to fill up the swirl pot until the fans came on, which is I think is unusual. During the last month of driving the temp guage in the car (on the Rover sender, not the TVR one) never went over 95, but I now think that the fans must have been on all the time as I saw earlier today.
During this, the idle was a steady 950 rpm and I took this opportunity afterwards to also check the base idle which needed a slight adjustment.
If the coolant was low could it be that these higher temperatures causing this erratic idling?
I also don't understand how it needed so much coolant, and why there was such a large air pocket in the swirl pot even though there was a couple of inches of coolant in the expansion tank.
Edited by jazzdude on Sunday 12th May 15:18
The airlocks are usually in the inlet manifold area near the temp sensor where there is an area the water doesn’t circulate very well.
When the pro’s bleed the water system they have a screw on type filling bottle with a small inlet that connects to the small pipe coming off inlet manifold in the temp sensor area, this allows water and air to bleed out the inlet and into your filling bottle via this pipe.
Just opening the pipe won’t work as the water needs to circulate until all air is expelled. Simply make an adaptor and some long pipe and put that pipe into your filling jug.
I then run the engine upto temps and keep revving it to increase pressure from water pump and this usually removes the last bit of air. Soon as fans kick in and out, you should be done, don’t get it to hot or it will boil over and draw more air back in.
This is after I’ve bled rad first.
I’d say your problem has been an air lock as it causes all these symptoms from my experience.
Pic of pipe.
Click on image then click again until image scrolls down page and it might be focused enough to just see I have a Stainless Allen type bolt screwed into my short pipe (100mm) which goes directly into inlet manifold. Make sure that pipe has a good seal as when it cools down it can draw air back in.
Hope that helps.
When the pro’s bleed the water system they have a screw on type filling bottle with a small inlet that connects to the small pipe coming off inlet manifold in the temp sensor area, this allows water and air to bleed out the inlet and into your filling bottle via this pipe.
Just opening the pipe won’t work as the water needs to circulate until all air is expelled. Simply make an adaptor and some long pipe and put that pipe into your filling jug.
I then run the engine upto temps and keep revving it to increase pressure from water pump and this usually removes the last bit of air. Soon as fans kick in and out, you should be done, don’t get it to hot or it will boil over and draw more air back in.
This is after I’ve bled rad first.
I’d say your problem has been an air lock as it causes all these symptoms from my experience.
Pic of pipe.
Click on image then click again until image scrolls down page and it might be focused enough to just see I have a Stainless Allen type bolt screwed into my short pipe (100mm) which goes directly into inlet manifold. Make sure that pipe has a good seal as when it cools down it can draw air back in.
Hope that helps.
Edited by Classic Chim on Monday 13th May 10:10
On other occasions where I have checked the water level in the swirl pot, with the cap on the expansion tank still on, the coolant level in the swirl pot is more or less level with the thread for the brass socket.
I'm not sure if the big gap appeared as I had the cap off the expansion tank, and thus the coolant flowed through the system and started filling up the expansion tank. I didn't think to check that, to be honest, so all I can do now is keep an eye on the level in the expansion tank for the next few days and perhaps at the weekend, open up the swirl pot again, but with the cap still on the expansion tank, and see if the level is still at the top, as it should be.
Driving the car this morning though, the idle behaved itself perfectly and did not rise at all, so one of the measure I did yesterday cured it, trouble is, not sure what.
I'm not sure if the big gap appeared as I had the cap off the expansion tank, and thus the coolant flowed through the system and started filling up the expansion tank. I didn't think to check that, to be honest, so all I can do now is keep an eye on the level in the expansion tank for the next few days and perhaps at the weekend, open up the swirl pot again, but with the cap still on the expansion tank, and see if the level is still at the top, as it should be.
Driving the car this morning though, the idle behaved itself perfectly and did not rise at all, so one of the measure I did yesterday cured it, trouble is, not sure what.
IGNORE my comment (2 inch gap can be normal) it’s just someone once said that!!!
I seem to think since I replaced my swirl pot bolt there is no longer a gap, water sits at the top of pot and I no longer have air in the system.
I’d check that as soon as the car is cold!
Did you bleed through that small pipe???
I seem to think since I replaced my swirl pot bolt there is no longer a gap, water sits at the top of pot and I no longer have air in the system.
I’d check that as soon as the car is cold!
Did you bleed through that small pipe???
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