Hello everybody,
I am experiencing an interesting phenomena on my Volvo:
After I drive on the highway, even for short period of time, when I return to city driving the idle has increased to about 1500 rpm. If I switch off and restart the engine, idle goes back to normal.
My engine is Turbo on a 91 940SE. Any clues?

Thanks a lot, David


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79 244 ; 91 240DL ; 91 POLAR ; 91 940SE Wagon

Check the continuity on your Throttle Position Switch per FAQ instructions in Engine- Sensors: high idle is often due to TPS failure.

How about the operation of IAC valve. Is this the only time that the idle is different from normal. I have two 940SEs and each idle differently. The wagon operates slightly higher than the sedan at around 850 rpm.

If you do look at the tps yuo could condider cleaning the contact points and the track that those points travel on. Both of these areas get dirty with crud in time ---that could be the problem ..Also you might want to clean the whole throttle throat --get the built carbon out and pay special attention to the 2 small orifices in the throat--they also get plugged with carbon build up over time. Let me know if these ideas help ______ALWAYS LEARNING

Thanks for the input. Regarding the intake manifold, I just cleaned a month ago the Throttle Body (with special attention to those 2 little holes) and changed the gasket. The TPS switch is clicking correctly, but I will double check it with the meter.
I was more thinking in the way of a faulty lambda sond (O2 sensor) or something that sends the data to the computer. Because when I reset the computer by turning the engine off and then on the idle goes back to normal. Therefore if it was a switch sticking in open position it will still be idling high, instead it must be a condition that occurs only at high RPM for an extended period of time...
I will also check the O2 sensor....

But many thanks for the brainstorming :-)

David
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79 244 ; 91 240DL ; 91 POLAR ; 91 940SE Wagon