IAC, Do I need it?

[Griffinr]

When I bought my car (2.9 S3) the idle air control valve was disconnected as it was holding the revs too high when the throttle was closed. Running disconnected was ok but gear changes where a bit harsh due to the revs falling off too quickly.
I have now cleaned and adjusted the AFM's, replaced the throttle pot and checked all the resistances and outputs from the sensors and the car is running well including just enough throttle hold to make smooth changes.
However I still can't connect the IAC as it still holds the throttle too high.
So the question is, do I really need it? as the only thing I can think of now is to try an alternative ECU.

[Roy C]

Have you tried cleaning it? The air bypass valve is prone to getting gummed up.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...

The valve acts as a choke, so if you leave it disconnected the car will run poorly when cold.

[tvrgit]

Also - if you've had bits disconnected, sometimes the ECU needs to reset itself, because it has configured adaptives to compensate for missing information, and it needs to forget them.

I would try disconnecting the battery for 10 minutes or so to erase the ECU memory.

Then reconnect and start the car - now it's starting from its base map. See what it's like then.

Some 2.9 cars (including mine) open the ISCV following such a reset, and run at a higher than normal idle, because they don't know how hot the engine is. To fix that, leave it idling until the fans cut in and go off again - now it knows where "hot" is and where "cold" is, so seems to reset its range accordingly. Next time you use it, it won't hold that high idle once the engine is warm. I don't know why that works, I only know that it does!

If that doesn't work, have you tried taking off the ISCV, and cleaning it out with carb cleaner? Clean out the airways in the throttle body as well - and it might also be worth taking off the air hoses and cleaning the throttle butterflies as well, to make sure they are closing properly.

If you do, then watch that the little red plastic tube that fits in the cleaner nozzle, doesn't come out and disappear past the throttle butterfly. It takes a very long time and a large selection of spanners and swear words to get it out. Don't ask me how I know this...

[Griffinr]

I have cleaned out the throttle bodies and butterflies, the IACV and just about everthing else. Even bought a new IACV (which did prove that the orignal one was working).
Interesting what you said about resetting the ECU and letting it get up to temperature, I will give this a try as it has not been reset since I fitted the new throttle pot.

Rob.

[jimed]

It may be a silly question but did you set the new throttle pot up so it gives the correct voltages closed and at full throttle, etc. Tozerman did this with some good effect on his S a couple of years ago so could be worth trying as part of the process?
Jim

[tozerman]

jimed said:

It may be a silly question but did you set the new throttle pot up so it gives the correct voltages closed and at full throttle, etc. Tozerman did this with some good effect on his S a couple of years ago so could be worth trying as part of the process?
Jim

Good point Jim, if the throttle stop screw is not set up correctly that can cause the problems you have with the too fast idle, there is a thread on here with a link to a V6 diagnosis pdf file (courtesay of TVRGIT) that works a treat, when I set my car up acordingly the difference was vast, worth a try.
Cheers.....Tony..

[Gerald-TVR]

'Ere it is

tvrgit said:

I've now fixed the link in that thread, for anybody wanting the diagnostic sheet it's at

http://www.andrewc.org.uk/tvrgit/ford29diagnostics...

[Griffinr]

Thanks for all the info guy's I will do a bit more checking and setting up and see how we go. A bit side tracked at the moment tho' as I have to change the clutch on my lads Bravo as his car maintenance skills are not quite up to it yet. Interesting failure though, the center has sheared out of the friction plate.

Rob.

[Griffinr]

Gerald-TVR said:

'Ere it is

tvrgit said:

I've now fixed the link in that thread, for anybody wanting the diagnostic sheet it's at

http://www.andrewc.org.uk/tvrgit/ford29diagnostics...

Thanks for the link, I finally got around to trying to sort my idle valve problem. Found a big air leak on the servo vacuum pipe and have checked, cleaned and set everything as advised in the diagnostics article. Car is running much better but still can't connect the idle valve (now have a new one) as it holds the revs to high on gear changes.
Anyone got a spare ECU I can try? (local to Stourbridge preferably)

Rob.

[tvrgit]

Griffinr said:

Gerald-TVR said:

'Ere it is

tvrgit said:

I've now fixed the link in that thread, for anybody wanting the diagnostic sheet it's at

http://www.andrewc.org.uk/tvrgit/ford29diagnostics...

Thanks for the link, I finally got around to trying to sort my idle valve problem. Found a big air leak on the servo vacuum pipe and have checked, cleaned and set everything as advised in the diagnostics article. Car is running much better but still can't connect the idle valve (now have a new one) as it holds the revs to high on gear changes.
Anyone got a spare ECU I can try? (local to Stourbridge preferably)

Rob.

It's possible that the ecu has "adapted" to the readings it was getting before. It might be worth resetting the ecu by disconnecting the battery for a few minutes, and then reconnecting it - now you're starting from the base maps.

Some cars (mine included) then seem to need the range set, by letting the car idle until the fans cut in, then off again. If I don't do that, the idle speed sits too high, because it seems to think the engine is cold so it enriches the fuel mixture and lifts the idle speed.

If that doesn't work, then it's possibly the multi-connector that sits under the coil. on the right-hand rocker cover. It's famous for water ingress, so the ecu gets conflicting signals (again, maybe not realising that the engine has warmed up for example). You can try replacing it with a waterproof connector, or, as some have done, by soldering the wires directly together and losing the connector altogether: on of my jobs for this summer.

Just realised - I said most of that before. It was a month ago and I'm senile.

Edited by tvrgit on Sunday 21st February 21:38

[Griffinr]

Thanks for that, I'm going senile as well so I did'nt notice you'd said it all before.
I have reset the ECU each time after tinkering with stuff but I get the same symptoms, If you blip the throttle or when you change gear the revvs are held at 1500-2000 for about 3 seconds then drop to normal tickover. Trying another ECU is probably the easiest next step before I admit defeat and have the car professionally looked at.

Rob.

[kenpage]

hi i had similar problems with mine tried all of the above and what cured mine was the water temp sender unit,not the one for the gauge the other one on the plenium... worth a try

[Gerald-TVR]

Got a couple of ECUs if you want to borrow for diags your welcome (need a bit of notice as one insnt at home) and I'm local in Droitwich

Drop me a PM with your contact numbers

Norman

PS also got a Star Tester (untried) you could borrow as well

[Griffinr]

Gerald-TVR said:

Got a couple of ECUs if you want to borrow for diags your welcome (need a bit of notice as one insnt at home) and I'm local in Droitwich

Drop me a PM with your contact numbers

Norman

PS also got a Star Tester (untried) you could borrow as well

Cheers Norman that would be a big help, perhaps next weekend I could pop over, I'll give you a mail.

Rob.

[Gerald-TVR]

Griffinr said:

and have the car professionally looked at.

Rob.

Have been told of someone in Covenrty (by Adrian Venn) who understands these things

[Gerald-TVR]

Comments from fordpower.org.uk

check for air leaks, if you dont find a air leak, replace the ISCV. its either leaking or stuck.

and yes, its needed. by disconnecting the ISCV, the ecu goes in limp home mode.

Plus more from fordpower

Or the ISCV caused too much problems and they set the throttle up higher. Make sure the TPS is set properly, and the throttle itself. It should run at 550 rpm without ISCV.

If it runs higher look for air leaks like Paul said. If no airleaks present, turn down the throttle stop so it runs at 550 RPM on a warm engine. Then connect the ISCV. It should run at 630 RPM

if the TPS is not adjusted properly, the engine can run to high. but the rpm also keeps hanging around 1500 rpm for a few seconds, if you close the trottle. the tps needs to have 0.9 volt.

for the 12v, like jurgen said: disconnect the ISCV, adjust the trottle screw so the engine runs at 650 and the tps is at 0.9 volt. connect the ISCV, the engine should start to run at 800 tp 850 rpm

Edited by Gerald-TVR on Sunday 7th March 07:55

[Griffinr]

Its FIXED!!
Thanks for all the suggestions guy's and to Norman for loan of the star tester and ECU.
Star tester showed no faults and the car ran the same with the alternative ECU. Could find no more air leaks so I figured it must be throttle setup. Slackened the throttle stop right off and the roller in the linkage and made sure the butterflies were completely shut. Carefully adjusted the stop and the roller started it up and its running fine. Had done this several times before but must have not been careful enough.
To run properly the throttle has to be completely shut at tickover, all the air required for tickover is let in through the idle valve.
Oh well, a little further up the learning curve, till tomorrow when i've forgotten again!!

Rob