Idle engine rev

[team9]

I am having an issue with my '89 325i. At idle, the engine will rev from 1k to 2k RPM's over a 3 second time frame, then drop back to 1k and start reving again. Is this an idle control valve problem or maybe an oxygen sensor problem?

And yes, I have done a search, but couldn't find any other threads with this similar problem.

[nando]

surging idle is an ICV usually - not neccesarily the valve itself, but the entire system that relates to it. That is, a properly working and adjusted TPS (should click when the throttle is closed), throttle stop not tampered with (it's not an idle adjustment), functioning ICV, no major vacuum leaks, etc.

it also helps if the AFM, CLT sensor and O2 sensor are working (these are primarily how the computer decides how much fuel to give) but an O2 sensor alone isn't going to cause a surging idle.