I posted a topic on my 1989 405Mi16 which tends to idle at high RPM at stop light etc. Previous posts suggested cleaning the control valve which my mechanic did with no change. Then someone kindly responded and suggested checking for problems with air intake. My mechanic just did that, and nothing significant was found.
I have confirmed (by observation) that my car will start idling at high RPM only when it warms up or during hot days EVENTHOUGH I don't see any significant change on the temperature gauges (coolant and engine oil). Does this mean something significant about the source of the problem.
Another question, is how often should the control valve be replaced ?? Is it a common problem where the entire control valve should be replaced (at $220).