Motronic Magic

[Seric]

So I've dug through the threads on idle problems and didn't find anything that looked similar to my problem. There is even an article in this month's Panorama that deals with Motronic, but it didn't really dive into the subject.

Symptoms;

Starts fine at any temp.

Cold idle works fine.

Cold idle quits as expected, then idle goes to 900-ish.

A few minutes later the idle will go up and bounce between 1150 and 1200+ and settle back down to 900 after a few minutes.

If the car is at operating temp, it takes longer for the idle to settle down to 900. I am thinking it's the Cylinder Head Temp unit, since it seems to start doing it when just as the engine gets warm. I have read that the idle mix could be to lean but that was more of a problem only when running hot.

Other than that, the engine pulls strong all day.

Danke

[BlueSideUp]

Have you tried unplugging the o2 sensor? A local guy here in SoCal had a bad o2 sensor causing an idle problem. The o2 sensor starts working once the engine is warmed up so it may be your problem.

[Seric]

I will give that a shot tonight. Thanks!

[rusnak]

The workshop manual from Bentley Publishing covers the diagnostic procedures very well. You'll need this manual, a digital multimeter, and some basic tools. It's like learning to read. Until you learn how, you're just guessing.

Beyond that, you should check the vacuum hoses and crankcase ventilation hoses for cracking. Also check the intake manifold bolts for tightness. The odds are you have a vacuum leak, bad O2 sensor, ICV, or CHT sensor. I'd say about 90% of the time it's one of these things.