[timfisher64]

I've seen posts about this problem on multiple sites, but have not been able to get a solid answer.

My BMW 2008 328i has a mildly rough idle in the 600 rpm - 625 rpm range. When the A/C is on the condition does not exist--only when the A/C is off. Fuel mileage is great with 30mpg Highway and 22-23 mpg City. Pick-up and performance is good. The computer is not throwing any codes.

I cleaned the Mass Air Sensor twice--so that's not it.

I've heard it could be the eccentric valve sensor which I had replaced a few years ago. I've heard it could be engine mounts. It drives me nuts that whenever the A/C is on, the car idles like buttah.

Anyone know what the problem is? What do I need to do to definitively diagnose the problem and cause?

 

[acoste]

It drives me nuts that whenever the A/C is on, the car idles like buttah.

That's because with the AC on the engine rpm gets raised by 150-200 rpm.

 

[acoste]

I think you have a little air leak somewhere.

 

[Gambleratheart]

My symptoms are the same but it happens only when AC is on and at a stop sign. Your issue is when AC is off. That is interesting. I have changed both VANOS and that doesn't solve the problem.

 

[CALWATERBOY DUE]

The computer is not throwing any codes.

How do you know?