Strange Idle Behaviour

[M31]

I had the exact same issue on my '02 S last week. Idle would go up to 1500 then down to 800 on it's own without my foot on the gas. My local garage pulled code P0507 on the diagnostic (idle control at stop) so they removed and cleaned throttle body. All was well for about 24 hours and then all hell broke loose! While waiting at a red light idle starting racing again and white smoke began billowing out the tailpipe like a giant refer from a Cheech & Chong movie! Turned out to be the infamous air/oil separator that I've been reading about on this forum. Returned to garage and mechanic found 15" of vacuum at the dipstick when there should be no more than .25" at any time according to him. Replaced the air/oil separator, cleaned the throttle body again which allowed it to idle around 700-800 consistently. It's been a week and no further issues so I suspect it was the air/oil separator from the start which prevented the throttle body to close in the first place. :ah: