robself705

This started happening a while ago and I have read a lot of threads about this with no definitive answer. It is usually around 750-1250 rpms. The needle moves around in that range for about 15-30 seconds and then settles down to 600 rpms. While it is bouncing the car vibrates almost as if it is misfiring.

Ideas?

I have cleaned the throttle body (it looked very clean) and the MAF looks perfectly clean too. I have used many gas stations between now and when it started. I am about to change the air filter (it is overdue) so that could be it, but it seems too violent for that.

br4d

crankshaft sensor, slight air leak, could be a whole load of things, check the rubber pipes to the intake manifold for cracks, even the breather pipes as they perish over time,
have had a few issues with my e46 330ci n your engine is the newer one to mine so must be similarish
hope this helps

luigi524td

Could be something as simple as a loose/cracked vacuum hose or incorrectly fitted oil filler cap (fairly common by the way) - OR, something electronic/ignition related - OR whatever

Might help if you provide your car's mileage and service / repair issues history?

10294545bmw

I had the same issue with an idle fluctuated around 530 to 600 RPM on my 06 530i with 135,000 miles on it. I just replace CVV oil trap and two insulated hoses and it went away. Engine runs like new now.

robself705

I might have to try that at some point. It isn't too bad right now and I don't really have the time to do it but I will have to add that to my list.

seanjordan

It seems to me to be an air leak. I have the issue and was a vacuum hose.

10294545bmw

Do the smoke test with an open throttle and see where is it coming from.

srschang

I have a 2008 528Xi that does the same thing. I bought the car with 9000 miles 3 years ago, can't remember if it did it early on or not. It's done it for the last couple years, the car now has 91,000 miles and it hasn't gotten any worse. I recently bought a 2008 Z4 with 18,000 miles, it has pretty much the same engine, and it does it also. They both rev between 700 and 1200 rpm for the first 30 seconds or so when I start them cold in the morning, then they smooth out & run fine. Since both cars do it, I guess I'm not worried about it.

mrfva

+1