I have a problem with idling. Symptoms:
When idling with the transmission in "D", the engine speed will go up and
down (only ever reaching about 800 rpm) and may eventually die.
Oddly, if the A/C is on, it idles well -- it stay at about 800 rpm.
I would think that this is a problem with the IAC valve, but the IAC valve
is only about 1 year old. I took it off and cleaned it with carburettor
cleaner and blew it out with comrpressed air, but this made no difference.
Usually, it will idle OK in neutral, but sometimes, after idling for a
while, it will start its cycle of the revs dropping to below 500 rpm and
back up to 800rpm, occasionally dying.
The problem is worse when the engine is cold, but it will also happen if
the engine is hot (usually, after idling for a short while).
Is this consistent with a bad idle air control valve or something else?