[Mk2] [Turbo] Engine revs raising on warm idle

[killerferret666]

Hi, summary below;

Rev3 engine / ecu.

Got the car out after the winter
Cold idle at about 900 - 1000rpm, as always has
When the warm idle kicks in revs raise to 1200rpm instead of dropping to about 800rpm.

* Looked for vacuum leaks and couldnt see any but still changed most hoses
* Checked for error codes bt none that im not expecting (error 42 as no ABS on car but expecting module)

been driving it fine since april, not loads of miles but just the high idle.
then couple weeks back out the blue revs at warm idle did what they should and dropped to 800rpm, was fine for a hundred miles or so now back to the 1200rpm.

* cleaned connectors.


Any tips, advice from anyone?

[Juliuswws]

Hi,

When the ECU is in learning mode after battery disconnect, you would have higher idle, but still, it should lower when the engine warms up.


I would check the following as the below have affect on your idle speed:
- Intake air temp sensor (~2.3k @ ~20C)
- Clean IAC valve + its setting on both side (spring, solenoid)


- Check TPS sensor with multimeter + butterfly valve - procedure is the service manual
A/C idle up valve also raises idle when A/C, lights, Defogger is on

Also , I read that that REV1-2 guys had idle problems due to leaking old caps in the ECU. REV3+ ECUs will be if not already affected as the time goes on.

Let us know

Cheers

[killerferret666]

Hi,

When the ECU is in learning mode after battery disconnect, you would have higher idle, but still, it should lower when the engine warms up.


I would check the following as the below have affect on your idle speed:
- Intake air temp sensor (~2.3k @ ~20C)
- Clean IAC valve + its setting on both side (spring, solenoid)
Image Replaced With URL For Quote https://i.imgur.com/y6syZBil.jpg
Image Replaced With URL For Quote https://i.imgur.com/uQE1JZdl.jpg
- Check TPS sensor with multimeter + butterfly valve - procedure is the service manual
A/C idle up valve also raises idle when A/C, lights, Defogger is on

Also , I read that that REV1-2 guys had idle problems due to leaking old caps in the ECU. REV3+ ECUs will be if not already affected as the time goes on.

Let us know

Cheers

Cheers for the reply. I think it will be the IACV valve...my first port of call.
I've got a new gasket so I'll whip it off Saturday and give it a really good clean.

Ecu should be fine I had all the capacitors changed for new ones.

TPS I've previously replaced so hope it's not that again!

[Juliuswws]

No worries, let us know.

Also, I gutted one cheap aftermarket TPS sensor out of curiosity, it was different internally than the genuine 89452-22090, and didn't pass all multimeter checks listed in the manual. Since then I got a genuine known good used one as a spare.

Cheers

[killerferret666]

No worries, let us know.

Also, I gutted one cheap aftermarket TPS sensor out of curiosity, it was different internally than the genuine 89452-22090, and didn't pass all multimeter checks listed in the manual. Since then I got a genuine known good used one as a spare.

Cheers

i have previously replaced the TPS sensor with a genuine one so although i need to multiemeter test properly as i kept slipping off the pins it seemed ok...


the IAC valve passed the multimeter test with opening / shutting, but I also did the test where you disconnect it when the engines hot and the revs dropped from the 1200+ to the 850-900 (slightly above the 800-850, but then the IAC will be slightly open rather then fully shut)


because I have an aftermarket filter etc... the breather pipe for the IAC is to atmosphere so I get a whistle when its sucking in air, so its like its not being turned off. At least with it disconnected the IAC valve is slightly open but not quite fully closed.


Im not sure where to go from here, i did check the wiring to the ECU and that seemed fine with multimeter reading along the wire.

checked the ECU and that looked ok, if i knew which cap id probably replace it.

[Juliuswws]

Two proper sized female blade connector+wire is perfect to attach to to TPS terminals and make measurements/adjustments.

I think IAC would need a disassembly and cleaning. A multi-meter check is not enough as there is no feedback from it back to the ECU.
I cleaned mine couple of years ago as a preventative maintenance. It wasn't seized, but had a little resistance (mechanical) due to some carbon buildup.





I would remove the throttle body and clean it all. You can also check/adjust butterfly valve and TPS at the same time. IAC is adjustable on both sides. Very little adjustment on the solenoid side, more adjustment on the spring side (^^^second pic with the spring removed)

The cap I remember seeing on a REV1 or 2 ECU was in the middle of the main board. More less where C823 is on our ECU.

Cheers

[killerferret666]

Two proper sized female blade connector+wire is perfect to attach to to TPS terminals and make measurements/adjustments.

I think IAC would need a disassembly and cleaning. A multi-meter check is not enough as there is no feedback from it back to the ECU.
I cleaned mine couple of years ago as a preventative maintenance. It wasn't seized, but had a little resistance (mechanical) due to some carbon buildup.


Image Replaced With URL For Quote https://i.imgur.com/kAvyUMVl.jpg
Image Replaced With URL For Quote https://i.imgur.com/vpDeEl9l.jpg

I would remove the throttle body and clean it all. You can also check/adjust butterfly valve and TPS at the same time. IAC is adjustable on both sides. Very little adjustment on the solenoid side, more adjustment on the spring side (^^^second pic with the spring removed)

The cap I remember seeing on a REV1 or 2 ECU was in the middle of the main board. More less where C823 is on our ECU.

Cheers

cheers for all this

I did clean it and take it off, I didn't remove the spring though on the other end actually thinking about it, but it was not stiff at all, very very loose and free actually.

I then did the test of putting 12v through it to open and shut it and no issue at all, opened and closed fine.

i'll check out the ECU again as I opened it up yesterday and all looked good.


At least I know the area causing the high idle now, just got to pin it down to the exact bit. ive left the IAC disconnected currently, fine driving it. Probably would start in this weather too actually but I can hold the throttle open slightly if I need to whilst I get to the bottom of it

[Juliuswws]

You are most welcome.

I found the topic I read years ago about this
https://www.mr2oc.com/threads/running-r ... ed.433011/

Not exactly your problem, but the guy at post #8 mentions "The cap pictured is part of the idle control circuit iirc"

Cheers