Idle Control Valve

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).

 

Hi,

I remember I suggested that.

No luck here.

Well, you mean the coolant gauge won't move from the min position (60°C I
guess) ? It may be interresting, as it could show a faulty coolant sensor. I
don't know if it is the same for coolant temp gauge & ECU, though.
I even can't remember where this sensor is (I hope other contributors know),
perhaps someone here have caracteristic voltages you could measure to ensure
it is correct.

When it fails.

Not that common on 405s, AFAIK. Anyway, keep in mind your car is 15 years
old, i.e it may well happen.