8 valve idle problem

My 155 8v idles fine when cold.

When it gets to about 70ºC the idle gets lumpy like it's got funky cams on it.

Generally the car drives fine although I feel it should be quicker through the revs.

Checked for air leaks in the induction, everything has been off and resealed from the intake manifold forward.

The idle is also a little high (about 900 - 950 rpm).

AFM is good and so is the ICV.

I'm suspecting it might be the engine temp sensor telling the ECU that the engine is colder than it really is, so it's overfueling slightly when warm. I'm pretty sure the Lambda is OK as on constant throttle the car is smooth.

What are your thoughts ??

Well, I would have said the AFM, but you said that was okay...

yeah it's a refurbed unit and it tested OK when I measured the resistances etc. It's also the 3rd unit I've tried on the car

had a similar problem on my 8v. turned out to be a broken piece of hose way back down the air track. Ended up replacing lambda and ICV and all sorts. the hose that was broken was the one just after the air flow sensor meter thing between that and the throttle valve. Never would have thought something back there would be important but it fixed it. Good luck finding your prob.

Thanks for that lostinflyz.

I've checked that hose a few times and I know they can crack at the "flexi" part, but it appears to be fine.

The thing that is strange is the car only does it once the temp has reached 70ºC.
Saying that, the symptoms to me are what I would associate with an air leak or weak mixture, but I can't find an air leak anywhere

what should it idle at cos mine idles at 900-950

Still got a problem Marlon? Could it be a crank position sensor thats on its way out maybe?

It's the temp thing that interests me here, I think it could be a throttle body problem, maybe the stepper is on the way out.

As I understand the ecu ignores the lambda until the temp is 70.

Originally Posted by alfa_nine

As I understand the ecu ignores the lambda until the temp is 70.

Never heard that one before, but I can understand why.