My S on mornings where the tempature is 55 degrees or below will start oscillating the idle between 1500 and 2000 rpm for about 20 seconds. This occurs after it has been started and running at 2000 rpms for a minute or so. Once the motor is hot, it hesistates when launching from idle and appears to run too low of RPMs.

What I have done is cleaned the IAC from the instructions on the site. This didn't do anything and the IAC wasn't real dirty anyhow. Does anyone have a suggestion?

 

Had the roughly the same problems you stated and I cleaned the IAC which was pretty dirty and the symtoms went away slightly and then after a bit got worse. So I just replaced the IAC and all problems were solved. Drives and idles like new (and no hesitation...bad IAC motor that attaches to the valve(i think). Just thought I would share my issues with the IAC.

Mat