Still Chasing idle issue - any further thoughts
Discussion
glenrobbo said:
phillpot said:
AMDBSTony said:
Hate this time of year as all cars laid up till spring/summer.......
Not mine 
I don't think I could go all the way through to May without going out for a blast in Austin. There are too many wonderful opportunities on bright sunny autumn/ winter/ early spring days with clear blue skies and lovely open twisty country roads: life's too short not to enjoy it while you can!
Rust is not a friend of older cars - hence why I keep them all tucked away over the rain and salty periods.
having just had rough idle problems discovered that both the airflow meters have a temp sender but only one is used they can be checked by simply swopping over the plugs so that the system uses the temp sensor in the other meter.I took out the main water temp sensor and tested the resistance to temp comparison, mine was ok but it is the main info sensor for the ecu cheers keith
Well, I have been working on this high idle problem and have officially got no further whatsoever. I made a new gasket and refitted the throttle body using blue Universal Hylomar, replaced the water coolant sensor for a shiny new one and swapped the AFM connections around to rule out that temperature sensor. It is still running exactly the same...
To aid in further diagnosis I have recorded these two videos.
This first one is the car idling steady at 2000 rpm with the ISCV connected. I quick blip of the engine shows that despite the throttle being on the stop (which is fully closed having inspected the throttle butterflies) the engine takes a couple of seconds to return to the high idle. When the ISCV is disconnected it returns to a nice 900 rpm.
The second one just amplifies the fact that a quick blip of the throttle (you can see it returning quickly to closed) does not equal a quick blip of the revs with the ISCV connected (blips perfectly with ISCV connected).
What on earth could be causing this??!!
To aid in further diagnosis I have recorded these two videos.
This first one is the car idling steady at 2000 rpm with the ISCV connected. I quick blip of the engine shows that despite the throttle being on the stop (which is fully closed having inspected the throttle butterflies) the engine takes a couple of seconds to return to the high idle. When the ISCV is disconnected it returns to a nice 900 rpm.
The second one just amplifies the fact that a quick blip of the throttle (you can see it returning quickly to closed) does not equal a quick blip of the revs with the ISCV connected (blips perfectly with ISCV connected).
What on earth could be causing this??!!
Well I have just spent the morning poking and prodding with a multi-meter (the Pico piercing probes are brilliant!) and although I'm still a long way from finding what the problem is, I hopefully am a little closer to find out what the problem is not. So here is what this morning proved:
• Impedance between ECU ISCV output (pin 21) and ISCV connector is only around .2 ohm in both directions, so no diode in yellow and brown signal wire. ECU is however definitely connected to ISCV.
• On the 12 volt side that also leads to ignition, there is negligible resistance in either direction from out of ECU to both sides of main connector (right up to ISCV input). Doesn't appear to be a diode here either.
• Resistance across the ISCV terminals is the same in both directions (think it was 12 ohms), so no internal diode (which is apparently on some newer cars); it would appear that there is no diode at all in the system.
• When the voltage across ECU pin 21 (ISCV) and ECU ground is measured, it only reads 2-2.3 as opposed to the +8 to +11v with engine running that is suggested here. Funnily enough this is the same from directly out of yellow signal wire of ISCV to battery ground. The black feed that runs to the ignition and ISCV reads a nice 12 v.
• Coolant temperature sensor looks spot on (1.8v @50 deg decreasing with rising temp. 60 deg = 1.3 v).
• Air Temp Sensor also looks good reading 3.4 v @ 8 deg.
• Fuel pump control reads near as dammit 12v.
• 5v reference signal spot on.
• The TPS does seem to differ in voltage to what it says on the link above and on the popular mechanics article; mine reads only 0.27v when closed - 3.7 with WOT (versus a suggested 0.6 or .7 to 4.5v). Could this be part of the problem?
• Pin 30 transmission in gear signal reads 5v no matter what selection, but doubt this has much to do with things?
So I guess the unanswered questions are:
1) Will adding a diode make all the difference? The popular mechanics article says "there is a diode fitted across the ISC circuit (in between pin 21 of the ECU and the supply from the main relay)" Where is this 'main relay' that it mentions?
2) Why is my ISCV voltage reading significantly less than what is suggested elsewhere?
3) Is the low TPS voltage likely to be messing everything up?
I'll pop out to the garage and have a good dig around for a spare TPS as a starter but not hopeful that that will make much difference as the previous owner has already done this. Again, I welcome any input that may finally help me nail down this problem!
• Impedance between ECU ISCV output (pin 21) and ISCV connector is only around .2 ohm in both directions, so no diode in yellow and brown signal wire. ECU is however definitely connected to ISCV.
• On the 12 volt side that also leads to ignition, there is negligible resistance in either direction from out of ECU to both sides of main connector (right up to ISCV input). Doesn't appear to be a diode here either.
• Resistance across the ISCV terminals is the same in both directions (think it was 12 ohms), so no internal diode (which is apparently on some newer cars); it would appear that there is no diode at all in the system.
• When the voltage across ECU pin 21 (ISCV) and ECU ground is measured, it only reads 2-2.3 as opposed to the +8 to +11v with engine running that is suggested here. Funnily enough this is the same from directly out of yellow signal wire of ISCV to battery ground. The black feed that runs to the ignition and ISCV reads a nice 12 v.
• Coolant temperature sensor looks spot on (1.8v @50 deg decreasing with rising temp. 60 deg = 1.3 v).
• Air Temp Sensor also looks good reading 3.4 v @ 8 deg.
• Fuel pump control reads near as dammit 12v.
• 5v reference signal spot on.
• The TPS does seem to differ in voltage to what it says on the link above and on the popular mechanics article; mine reads only 0.27v when closed - 3.7 with WOT (versus a suggested 0.6 or .7 to 4.5v). Could this be part of the problem?
• Pin 30 transmission in gear signal reads 5v no matter what selection, but doubt this has much to do with things?
So I guess the unanswered questions are:
1) Will adding a diode make all the difference? The popular mechanics article says "there is a diode fitted across the ISC circuit (in between pin 21 of the ECU and the supply from the main relay)" Where is this 'main relay' that it mentions?
2) Why is my ISCV voltage reading significantly less than what is suggested elsewhere?
3) Is the low TPS voltage likely to be messing everything up?
I'll pop out to the garage and have a good dig around for a spare TPS as a starter but not hopeful that that will make much difference as the previous owner has already done this. Again, I welcome any input that may finally help me nail down this problem!
Do you mean the "Electronic Diagnostics! Part 8" article from Car Mechanics 1995 ?
Here, on page 63, it does show a diode connected between ECU pin 21 and pins 37/57, which are connected to the main relay.
In the TVR diagram this diode is shown across the terminals of the ISCV, but is connected to ECU pin 58, so that's a bit confusing really.
Not sure which one is correct and I can't check mine at the moment as the body is hanging from the roof of the garage.
Here, on page 63, it does show a diode connected between ECU pin 21 and pins 37/57, which are connected to the main relay.
In the TVR diagram this diode is shown across the terminals of the ISCV, but is connected to ECU pin 58, so that's a bit confusing really.
Not sure which one is correct and I can't check mine at the moment as the body is hanging from the roof of the garage.
Yip, that is the one, the Car Mechanics article. See my predicament? I just don't know where to go from here! Is there some 2.9 Cologne V6 genius out there that I can take this too with what I have done so far and pay him to make it better?! I'd like to get it done myself over the winter both for the satisfaction, to learn more about the car and to save money (given how difficult it has been to identify the problem so far it may just be like throwing money down a well!), but I'm at the limit of my mechanical knowledge and the answers around the internet are drying up :-(
I haven't personally, but the previous owner did and he has put in a new servo and hoses too. All the same I'll give it a go this weekend to rule it out. I might look at putting in a 'new' ECU at some point to completely rule that out too, but all indications are that they are pretty bullet proof, so sadly not likely to make a difference.
ukflyboy said:
I haven't personally, but the previous owner did and he has put in a new servo and hoses too. All the same I'll give it a go this weekend to rule it out. I might look at putting in a 'new' ECU at some point to completely rule that out too, but all indications are that they are pretty bullet proof, so sadly not likely to make a difference.
Still seems like an air leak to me, but trying another ECU would a least rule it out. Probably someone on here has a spare one you could borrow.ukflyboy said:
Yip, that is the one, the Car Mechanics article. See my predicament? I just don't know where to go from here!
Have a look at the relays which are stuffed in next to the ECU. Check if you have a diode there. I remember seeing one on mine, but I can't remember exactly where. Maybe someone else can help here ?If you don't find one, maybe consider fitting one. A simple Silicon diode should do. Not exactly sure why the diode is there, but it will give you a fixed forward voltage of approx. 0.7V (threshold voltage) when the ISCV goes above this value.
Not sure how helpful this is but I just recreated your exact fault symptoms on my car. I put a feeler gauge between the throttle and the stop to increase the tick over then when you blip the throttle the revs stay high for a second or two before falling back.
This may be because the ISCV has a preset setting then when the ECU sees the tick over too fast on close of throttle it adjusts the ISCV hence the lag.
My money is still on an air leak or poor butterfly fit.
This may be because the ISCV has a preset setting then when the ECU sees the tick over too fast on close of throttle it adjusts the ISCV hence the lag.
My money is still on an air leak or poor butterfly fit.
ukflyboy said:
I haven't personally, but the previous owner did and he has put in a new servo and hoses too. All the same I'll give it a go this weekend to rule it out. I might look at putting in a 'new' ECU at some point to completely rule that out too, but all indications are that they are pretty bullet proof, so sadly not likely to make a difference.
Tried that with a different ECU that I borrowed, no change. Also I could never track down where the diode was and stopped looking when I found somewhere on the internet that the diode was incorporated into the ISCV on later models.Still lurking and interested in answer to this if it ever gets sorted, I'll even keep an eye from Washington when I move there in the summer
Edited by mep12345 on Friday 27th November 16:33
Edited by mep12345 on Friday 27th November 16:34
Hey Mark, good to hear from you!
I read that about the diodes too but someone suggested that if the resistance is the same either way across the ISCV pins then there wasn't one internally in the ISCV which makes sense with my limited auto electrical knowledge (does that make sense to others?). From reading around though, it looks like the diode is only there to stop a stray voltage spike from frying the ECU, so not likely to fix this issue.
I'll keep trying to get it sorted over the winter and if I am no closer to a solution, put everything back together and hopefully enjoy another summer of ISCV free smooth running! It would be lovely to have it all working as it should though. Look at the bright side, when/if I fix it I will no that everything else is working tip top too! Might have to head down the leak route again for a bit...
Great to hear about your posting to Washington, that will be a great lifestyle change and should be a pretty interesting job for a few years too. Congrats, very jealous!
I read that about the diodes too but someone suggested that if the resistance is the same either way across the ISCV pins then there wasn't one internally in the ISCV which makes sense with my limited auto electrical knowledge (does that make sense to others?). From reading around though, it looks like the diode is only there to stop a stray voltage spike from frying the ECU, so not likely to fix this issue.
I'll keep trying to get it sorted over the winter and if I am no closer to a solution, put everything back together and hopefully enjoy another summer of ISCV free smooth running! It would be lovely to have it all working as it should though. Look at the bright side, when/if I fix it I will no that everything else is working tip top too! Might have to head down the leak route again for a bit...
Great to hear about your posting to Washington, that will be a great lifestyle change and should be a pretty interesting job for a few years too. Congrats, very jealous!
Does this help in any way ?
Pages from EEC IV Ford Fuel Injection and EEC Book
It says here that the ISCV is supplied with digital pulses from the ECU. Maybe you need to replace the wire which connects these two, as this could also affect the function. Just an idea.
Pages from EEC IV Ford Fuel Injection and EEC Book
It says here that the ISCV is supplied with digital pulses from the ECU. Maybe you need to replace the wire which connects these two, as this could also affect the function. Just an idea.
Griffinr said:
Just a thought but have you tried clamping off or plugging the pipe to the servo, just to eliminate issues in that area. Obviously you would not want to drive it like that.
Rob.
^^^ what Rob said, with a twist - plug off the crank breather hose. Mine was heater hose and collapsed when warm, which messed up the idle because the engine was missing that somewhat regulated, unmetered flow from the crankcase, so the ISCV would make up for it in spades. A new hose and PCV later and my mystery was solved.Rob.
Thanks for the ongoing help folks. I'm gonna be busy on best-man duties for a couple of weeks but will try progress things when I get the time.
Tim, cant see any obvious diodes around there so might look at sticking one in the system. I figure it can't really do any harm; the only problem is, I've not managed to figure out exactly where is is supposed to go! Thinking it just needs to be between pin 21 at the ECU and the ISCV, with current flow in that direction? Anyone know what sort of diode I'd need? Thanks for the link, I'll get that read soonest.
Rob, your recreation of the fault is very interesting, particularly the revs staying higher for a second or two. My gut still seems to think air leak too, so I'm just trying to find somewhere that can to a proper smoke test or similar. I'll keep you posted...
Tim, cant see any obvious diodes around there so might look at sticking one in the system. I figure it can't really do any harm; the only problem is, I've not managed to figure out exactly where is is supposed to go! Thinking it just needs to be between pin 21 at the ECU and the ISCV, with current flow in that direction? Anyone know what sort of diode I'd need? Thanks for the link, I'll get that read soonest.
Rob, your recreation of the fault is very interesting, particularly the revs staying higher for a second or two. My gut still seems to think air leak too, so I'm just trying to find somewhere that can to a proper smoke test or similar. I'll keep you posted...
Haven't read the whole piece so I don't know if you've considered this....
http://www.pistonheads.com/gassing/topic.asp?t=900...
Certainly was the cause of my idle issues. A new speed sensor cured it straight away.
http://www.pistonheads.com/gassing/topic.asp?t=900...
Certainly was the cause of my idle issues. A new speed sensor cured it straight away.
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