M20b25 Cold Idle problem

[max]

Hi guys, I've had an 2.5 fitted by James at JFI Classics, I haven't picked it up yet because he is having trouble with the idle when cold. It starts first time, then after a few minutes it will stall. And it will do this until it's warm, then it runs fine. He said that if you just set off in it and didn't stop until it was warm you would never know!
He's changed the temp sensor, idle control valve and neither made any difference. The ECU has been chipped ( it was discovered when wired up).
I'm putting a lot of money into this car, as I haven't got time to do stuff to it myself, and I'll be a bit disappointed if it's not running right.
Any advise would be amazing.
I already feel like a bit of a fool spending so would on it, when I could have waited for one that was done to turn up!
Help!
Cheers, Max

[gazzab1978]

try the lambda sensor, these can cause stalling when cold if there on the way out, did you drive the doner car before the engine was removed was it running ok

[max]

James supplied the engine, so I know nothing of its history.
The lambda sensor is tapped into the exhaust right?

[Jeroen]

Correct. That is a likely problem. Other ones that come to mind:
- throttle position switch (defective or not getting into idle position) > not likely tho if its ok when warm
- temp sender wiring causing incorrect signal to ECU
- intake air temp sender inside the AFM
- TB base adjustment
- vacuum leak

Do you have exhaust gas analysis data during warmup?

[max]

I'm not sure what he's done with the lamda, the exhaust is pretty knackered, so I'm going to get a stainless one made.
I'll phone and ask him today. He did think it might have been the MAF?

[Jeroen]

Is it running on a MAF conversion or an AFM? AFM already mentioned above, if the problems are gone when the engine is warm the AFM itself is not a real suspect, but the built in intake air temp sender is. Exhaust gas data will also tell us a lot!

[max]

James is saying the m20 doesn't have a lambda?!

[Jeroen]

That is possible, rules than one out then haha. M20B25 was available with and without, and could have been deleted as well. Just make sure not to use a ECU with lambda control switched on or it'll run in emergency program.

[max]

The c02 levels are fine. And it runs fine when warm, if it was lambda or lack of, would would think it would run good at all?

[Jeroen]

Overly rich as a precaution.

With a defective temp sender (either intake air or coolant) the ECU usually is being told a very low temp, meaning it makes the mixture extra rich as well. If you adjust a warm engine to that, it may run too lean during warmup, that's why the exhaust gas figures cold/warmup/warm can give you more info on what is happening is it is likely it's running too rich or too lean during warmup.

Lambda control switched on on a setup without lambda may cause all sorts of issues as, together with the throttle switch, the ECU may be trying to adjust a erroneous lambda measurement. If the throttle switch is defective or badly adjusted, it may think the throttle is being operated instead of being idle.

We need as much as possible info though for example: only idle issues or does it also give problems through the rev range? Is is slowly improving during warm up or all of a sudden the problem is gone?

[max]

James thinks it might be the MAF. I've bought a second hand one, with the right numbers on, and he's going to try it today!!
Fingers crossed. ( I've said a little prayer to the Munich motor gods).

[gerrit323]

The idle control valve is controlled by the ecu but sometimes the resistance in the ecu for the icv is broken .. than changing the icv is no solution ..

I have the same problem on my 2.7 except mine runs a bit rough cold but doesn't stall

If you turn the ignition is 2nd position do you hear the icv or not at all .. if not no power and probably a dead ecu resistance ..

Rgds

Gerrit

[max]

Well, I'll be darned! I bought a used MAF from eBay, as James felt he had exhausted other options. I thought, "I might as well throw £65 at it to take something the MAF out of the equasion (but kinda thinking that there a chance the used one is no good either?!).
I thought that it wouldn't do a thing but to my surprise, (and James'), he texted me saying that it is now running sweet !
Hooray! Time to start enjoying it, and trying to forgot how much I've spent on it! But before that a stainless exhaust and a new set of boots!
Then no more spending...well maybe a retrim....and I'd love some BBS splits!?

[e21-Mark]