High idle driving me nuts!
Discussion
Folks, can you help please.
My 450 is intermittently idling at around 1800-2000rpm, so no engine braking and driving me nuts.
It will idle at the correct level when the car is stationary but if you lift the revs or drive off, the idle goes back up to 1800-2000rpm. Put the car in neutral whilst at speed and the idle will stay high until about 1 sec after the car comes to a halt, when it will drop to 900rpm or so again.
Pull off and the process repeats.
This causes no engine braking and makes me look like a boy racer revving at the lights.
Any ideas? The stepper motor is audibly retracting on ignition shut off. I can control the idle speed / stepper motor position with RG fine so that seems fine.
If I set the idle to 950 and then disconnect the stepper with the ignition on, all of these problems go away. No high idle and full engine braking and much less shunting.
Seems as though it is the control of the stepper rather than the stepper itself but I could be wrong.
RG once did show a road-speed sensor ECU fault code so wondering if this could be it. However, the speedo works fine.
Does the ECU use a different sensor to the speedo ?
Ta.
My 450 is intermittently idling at around 1800-2000rpm, so no engine braking and driving me nuts.
It will idle at the correct level when the car is stationary but if you lift the revs or drive off, the idle goes back up to 1800-2000rpm. Put the car in neutral whilst at speed and the idle will stay high until about 1 sec after the car comes to a halt, when it will drop to 900rpm or so again.
Pull off and the process repeats.
This causes no engine braking and makes me look like a boy racer revving at the lights.
Any ideas? The stepper motor is audibly retracting on ignition shut off. I can control the idle speed / stepper motor position with RG fine so that seems fine.
If I set the idle to 950 and then disconnect the stepper with the ignition on, all of these problems go away. No high idle and full engine braking and much less shunting.
Seems as though it is the control of the stepper rather than the stepper itself but I could be wrong.
RG once did show a road-speed sensor ECU fault code so wondering if this could be it. However, the speedo works fine.
Does the ECU use a different sensor to the speedo ?
Ta.
I Would still say stepper motor, just because you can hear it retracting doesn't mean it's retracting properly. Also if it's not moving as instructed by the ECU you wouldn't easily know. I would test it with the motor out the car and RG, to test it's full range of extension, but be careful not to let the pin come out. Then you can rule out if it's working or not. Even still I'd be tempted to borrow a known working one and test it
Does RG show the system going into idle mode? Drive it and take a log (actually not sure if the idle flag is in the log but you can easily check), and take a look at the idle mode indicator on the screen when the problem occurs.
There is probably more than one possible cause of not entering idle mode (and yes no road speed is one of them) but I think you need to establish if that is happening or not first.
There is probably more than one possible cause of not entering idle mode (and yes no road speed is one of them) but I think you need to establish if that is happening or not first.
I had a sticky stepper motor that used to do this.
It would start up fine then not long after idle would become erratic.
I’d noticed on ECUMATE at the time the numbers for normal operation of stepper would become higher when idle messed up suggesting stepper was stuck further out than it should be.
Turn off, stepper over pulses to ensure it’s fully back in and next start up it would be ok for a few minutes.
The only real way to be sure with steppers is to borrow a used and known working original and if all returns to normal it’s clearly a knackered stepper.
The problem occurs when you get a replacement ( copy) which can also be useless so def worth checking using a known example first imho.
It would start up fine then not long after idle would become erratic.
I’d noticed on ECUMATE at the time the numbers for normal operation of stepper would become higher when idle messed up suggesting stepper was stuck further out than it should be.
Turn off, stepper over pulses to ensure it’s fully back in and next start up it would be ok for a few minutes.
The only real way to be sure with steppers is to borrow a used and known working original and if all returns to normal it’s clearly a knackered stepper.
The problem occurs when you get a replacement ( copy) which can also be useless so def worth checking using a known example first imho.
The stepper will hold the idle high if either the throttle pot is showing the throttle is still part open- it its more than about 10%, or there is a speed reading when the car is NOT moving- so check when RoverGauge displays the car is in idle mode- and at this point the stepper should try and set the RPM to match the target idle. On a warm idle the stepper should be at about 30 to 40%, but if it drops near 0 you might have an air leak when things warm up.The ECUmate manual has an excellent bit on idle and stepper control- you can still download it here:
http://ecumate.com/docs/Ecumate%20inst.pdf
http://ecumate.com/docs/Ecumate%20inst.pdf
What made me think it wasn't a stuck stepper is that when the car is stopped, the idle always returns to normal within a second of stopping. If it were sticking this wouldn't always happen.
It seems like when the car is moving, the ECU is telling the idle to go high but don't understand why that would happen.
I have seen the Idle light come on on RG and the target idle rpm sounded reasonable.
So if I take RG for a drive, what am I looking for?
The idle light isn't going to come on when I'm driving.
The problem is high idle (1800-2000rpm) when driving. Revs actually go up as you change gear !
It also happens under initial startup sometimes. It will idle at 1800rpm for 5 or 6 seconds before dropping to something more sensible.
It seems like when the car is moving, the ECU is telling the idle to go high but don't understand why that would happen.
I have seen the Idle light come on on RG and the target idle rpm sounded reasonable.
So if I take RG for a drive, what am I looking for?
The idle light isn't going to come on when I'm driving.
The problem is high idle (1800-2000rpm) when driving. Revs actually go up as you change gear !
It also happens under initial startup sometimes. It will idle at 1800rpm for 5 or 6 seconds before dropping to something more sensible.
taylormj4 said:
What made me think it wasn't a stuck stepper is that when the car is stopped, the idle always returns to normal within a second of stopping. If it were sticking this wouldn't always happen.
It seems like when the car is moving, the ECU is telling the idle to go high but don't understand why that would happen.
I have seen the Idle light come on on RG and the target idle rpm sounded reasonable.
So if I take RG for a drive, what am I looking for?
The idle light isn't going to come on when I'm driving.
The problem is high idle (1800-2000rpm) when driving. Revs actually go up as you change gear !
It also happens under initial startup sometimes. It will idle at 1800rpm for 5 or 6 seconds before dropping to something more sensible.
That just sounds like a vacuum leak.It seems like when the car is moving, the ECU is telling the idle to go high but don't understand why that would happen.
I have seen the Idle light come on on RG and the target idle rpm sounded reasonable.
So if I take RG for a drive, what am I looking for?
The idle light isn't going to come on when I'm driving.
The problem is high idle (1800-2000rpm) when driving. Revs actually go up as you change gear !
It also happens under initial startup sometimes. It will idle at 1800rpm for 5 or 6 seconds before dropping to something more sensible.
Classic Chim said:
I had a sticky stepper motor that used to do this.
It would start up fine then not long after idle would become erratic.
I’d noticed on ECUMATE at the time the numbers for normal operation of stepper would become higher when idle messed up suggesting stepper was stuck further out than it should be.
Turn off, stepper over pulses to ensure it’s fully back in and next start up it would be ok for a few minutes.
The only real way to be sure with steppers is to borrow a used and known working original and if all returns to normal it’s clearly a knackered stepper.
The problem occurs when you get a replacement ( copy) which can also be useless so def worth checking using a known example first imho.
Seconded. I bought a cheap one for my last Chimaera in 2014 it would idle at 2000 rpm, ludicrous. Biting the bullet and paying £90 for a genuine one sorted it.It would start up fine then not long after idle would become erratic.
I’d noticed on ECUMATE at the time the numbers for normal operation of stepper would become higher when idle messed up suggesting stepper was stuck further out than it should be.
Turn off, stepper over pulses to ensure it’s fully back in and next start up it would be ok for a few minutes.
The only real way to be sure with steppers is to borrow a used and known working original and if all returns to normal it’s clearly a knackered stepper.
The problem occurs when you get a replacement ( copy) which can also be useless so def worth checking using a known example first imho.
I'm not saying all 'copy' ones are duff, others have had ones that worked fine, but I didn't.
I have a used stepper sitting on my desk. I suspect it's not the one taken out of my car when I converted to an Emerald ECU. I have a feeling that one was in the bag of ignition bits I loaned to a Griff owner who had running problems and was part of his solution that he retained, but I will check the man cave tomorrow.
Point is, you can have this stepper to try if you want, I just cannot guarantee it is a good one. It has a heavy metal body and has the numbers 73312A and B1463= stamped on the surround of where the electrical plug goes. PM me your address if you want to give it a try.
If I can find the other one in the man cave, that is definitely genuine TVR and i can send you that too. I was having running problems a few years ago, with the engine dying at every junction when I stopped, but only once the car was warm. I phoned Rob (V8D) to check a point about something he had installed on my car the previous year, and he, being the gent he is, said "bring it over, I will see if i can work out what's wrong". After an hour of getting nowhere he said under his breath "it MUST be the stepper", and which point I said "have you by any chance got a used original one in your bits shed?". He did, he installed it. Problem solved.
Point is, you can have this stepper to try if you want, I just cannot guarantee it is a good one. It has a heavy metal body and has the numbers 73312A and B1463= stamped on the surround of where the electrical plug goes. PM me your address if you want to give it a try.
If I can find the other one in the man cave, that is definitely genuine TVR and i can send you that too. I was having running problems a few years ago, with the engine dying at every junction when I stopped, but only once the car was warm. I phoned Rob (V8D) to check a point about something he had installed on my car the previous year, and he, being the gent he is, said "bring it over, I will see if i can work out what's wrong". After an hour of getting nowhere he said under his breath "it MUST be the stepper", and which point I said "have you by any chance got a used original one in your bits shed?". He did, he installed it. Problem solved.
This does sound very similar to a problem with high idle I had.
It turned out to be split in the small vacuum pipe that runs from the fuel pressure regulator to the plenum, near the stepper.
I found it quite by chance given that it's hidden, but it was a quick and cheap fix - good luck!
It turned out to be split in the small vacuum pipe that runs from the fuel pressure regulator to the plenum, near the stepper.
I found it quite by chance given that it's hidden, but it was a quick and cheap fix - good luck!
QBee said:
I have a used stepper sitting on my desk. I suspect it's not the one taken out of my car when I converted to an Emerald ECU. I have a feeling that one was in the bag of ignition bits I loaned to a Griff owner who had running problems and was part of his solution that he retained, but I will check the man cave tomorrow.
Point is, you can have this stepper to try if you want, I just cannot guarantee it is a good one. It has a heavy metal body and has the numbers 73312A and B1463= stamped on the surround of where the electrical plug goes. PM me your address if you want to give it a try.
If I can find the other one in the man cave, that is definitely genuine TVR and i can send you that too. I was having running problems a few years ago, with the engine dying at every junction when I stopped, but only once the car was warm. I phoned Rob (V8D) to check a point about something he had installed on my car the previous year, and he, being the gent he is, said "bring it over, I will see if i can work out what's wrong". After an hour of getting nowhere he said under his breath "it MUST be the stepper", and which point I said "have you by any chance got a used original one in your bits shed?". He did, he installed it. Problem solved.
Hi QBee, very generous offer thanks. I'd be reluctant to try another stepper if you're not sure it's the right type, in case I damage the electrics/ECU by fitting something with a different resistance or load but if you have a genuine TVR one, that would be awesome. The stepper has not been changed since I have had the car (i.e. around 17 years) but I have cleaned and checked its operation with RG before.Point is, you can have this stepper to try if you want, I just cannot guarantee it is a good one. It has a heavy metal body and has the numbers 73312A and B1463= stamped on the surround of where the electrical plug goes. PM me your address if you want to give it a try.
If I can find the other one in the man cave, that is definitely genuine TVR and i can send you that too. I was having running problems a few years ago, with the engine dying at every junction when I stopped, but only once the car was warm. I phoned Rob (V8D) to check a point about something he had installed on my car the previous year, and he, being the gent he is, said "bring it over, I will see if i can work out what's wrong". After an hour of getting nowhere he said under his breath "it MUST be the stepper", and which point I said "have you by any chance got a used original one in your bits shed?". He did, he installed it. Problem solved.
Sir Paolo said:
This does sound very similar to a problem with high idle I had.
It turned out to be split in the small vacuum pipe that runs from the fuel pressure regulator to the plenum, near the stepper.
I found it quite by chance given that it's hidden, but it was a quick and cheap fix - good luck!
That sounds interesting. I will certainly check that.It turned out to be split in the small vacuum pipe that runs from the fuel pressure regulator to the plenum, near the stepper.
I found it quite by chance given that it's hidden, but it was a quick and cheap fix - good luck!
I would have thought an air leak would cause the revs to gradually drop once the throttle was closed. If I run in neutral, the revs will remain high for as long as you like, only coming down when the car rolls to a near stop.
blitzracing said:
Id tend to agree about the leak but did you check the speed reading, throttle pot and stepper position and target idle with RoverGauge at idle? Post the results.
Will do. Sorry for ignorance but do I just hit record on RG and then take it for a drive then download teh results here somehow?taylormj4 said:
blitzracing said:
Id tend to agree about the leak but did you check the speed reading, throttle pot and stepper position and target idle with RoverGauge at idle? Post the results.
Will do. Sorry for ignorance but do I just hit record on RG and then take it for a drive then download teh results here somehow?Had one recently that would high idle 2k and despite all other readings being OK it would not go into idle mode. Turned out to be the ECU chip corrupt.
Steve
The OP should buy himself the above hose clamp type, this simple but invaluable tool is highly effective at helping you pin down a fast idle condition, it also hand down beats staring into the screen of your laptop waiting for an answer to pop out
For instance, if you use it to clamp the air supply hose to the stepper motor it really doesn't matter a jot what position the stepper motor is in.... because you'll be completely cutting off that path of air with your hose clamp!
If the idle drops you'll have immediately proved the issue relates to that path of air into the inlet manifold or the stepper motor, or what the ECU is telling it to do.... see no laptops required. Now work your way around the engine clamping off the various hoses subject to engine vacuum and you'll soon find the source of your issue... assuming it is indeed hose related of course.
Hoses subject to engine vacuum to apply the clamp check on would be:
1. The air feed to the stepper motor, as covered above
2. The crankcase breather hose, clamp the hose at the front of the plenum and as close to the plenum as you can
3. The small bore hose that supplies the fuel pressure regulator at the back of the plenum, again clamp as close to the plenum as you can
4. The brake servo hose, and yes you guesses it clamp as close to the plenum takeoff as you can
5. The carbon canister hose following the same rule of clamping as close to the plenum as you can
Always keep in mind an internal combustion engine is just a giant and highly effective vacuum pump, all it wants to do is draw air from the atmosphere and if allowed to do so will just keep sucking more and more air until either that path of air reaches a point where it becomes a restriction or the engine spins so fast a con rod will come out or the side of the block or valves start colliding with pistons as there is a point where valve springs no longer function as springs.
This is why we have a throttle, without it the engine would just run away with itself with disastrous consequences, the car would also be completely undrivable because the throttle butterfly is your only true means of controlling engine speed.
Have a go at clamping off those five hoses and always do so as close the the plenum/inlet manifold as you can, do check the general condition of these hoses and make sure their Jubilee clips are tight. Now we have Rover Gauge it's my opinion there's a general over eagerness to break out the laptop, I strongly recommend keeping things simple and returning the the basic diagnostic methods that have stood us in good stead for the last 100 years.
Clamping hoses is a simple, fast, and effective way to eliminate the above 5 key points of unwanted/excessive vacuum leaks common on a Chimaera engine. But this method only helps where hoses are concerned, so if after completing your hose clamp test you find your idle is still high you'll need to look elsewhere. Remember your engine is just a giant vacuum pump tying it's very hardest to find a supply of air from atmosphere, so if your hose clamp tests prove inconclusive do move on to other likely areas of air ingress such as the inlet manifold gasket, the plenum base, the forward facing pipe spur off the throttle body ect.
And of course the big one..... Your throttle butterfly rest position itself!!!!
A really badly adjusted throttle butterfly can even go overcentre which can cause all sorts of headaches and a potentially a high idle condition, even something as simple as a sticky throttle cable or mechanism is most definitely going to give you a high idle. Finally keep in mind the throttle butterfly is never fully shut, there is always a tiny preset gap between the edge of the throttle butterfly and the throttle body, this gap is critical!
Follow the above, and without any Rover Gauge software or laptop you've been able to very quickly check ten times more potential vacuum leak points than merely the stepper motor position. Indeed you'll probably have checked all these points before the guy with Rover Gauge has even plugged his laptop into the Lucas diagnostic port
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