New Z3 2.8 owner, rough idle?

[keenraven]

Hey there! Had my car a few days now, 1997 with 75,000 miles. It’s cold today, and I’m noticing a slight oscillation in rpm at idle — between 1000 and 1200 rpm.

Did a little forum searching, saw mention of O2 sensors and VANOS (though I don’t know what that is!).

I don’t really mind the issue if it’s not going to create larger problems. What steps should I take?

Thanks so much for any advice!

 

[Dre0415]

I'm willing to bet it's the main intake boot had exact same problem with mine. Give the main intake boot a squeeze and check for cracks. If you see cracks replace it and that should get you back running smooth. O2 sensors really shouldn't cause this type of problem on a 1997. Your definitely going to be looking at some sort of vaccum issue if I had yo guess. Does your issue fix itself when the car warms up?

 

[Dunkelgrun]

Could be any number of things but +1 on checking the intake boot. Mine looked fine from the top but had a big hidden crack on the bottom side... while you are there you can clean the gunk off the throttle body too, that can effect idle. Maybe buy a new gasket first so don’t have to reuse the squashed old one

 

[keenraven]

I'm willing to bet it's the main intake boot had exact same problem with mine. Give the main intake boot a squeeze and check for cracks. If you see cracks replace it and that should get you back running smooth. O2 sensors really shouldn't cause this type of problem on a 1997. Your definitely going to be looking at some sort of vaccum issue if I had yo guess. Does your issue fix itself when the car warms up?

Thank you for the input! I’ll definitely investigate the intake boot. The situation is strange — it has only happened once. I drove it 3-4 times yesterday, with plenty of time for the car to cool down in between; but the issue never reoccurred.

 

[Patryk]

I'm willing to bet it's the main intake boot had exact same problem with mine. Give the main intake boot a squeeze and check for cracks. If you see cracks replace it and that should get you back running smooth. O2 sensors really shouldn't cause this type of problem on a 1997. Your definitely going to be looking at some sort of vaccum issue if I had yo guess. Does your issue fix itself when the car warms up?

I had rough idle only on warm, since I bought the car. Mine had problem with o2 sensors. It turned out that the wiring was literally melted. Someone snapped the cable with gearbox mounting.