This just started happening with my 1990 Grand Marquis EFI 5.0.
After I start driving from my home and stop at a light, sign, etc., the car
starts idling very high with my foot on the brake. It changes on its own
because when I leave home it is idling fine. Sometimes the idle doesn't
change at all.
The most common time it happens is after I get on the highway and the car
was idling fine until I got to the highway, I drive approx. 60 MPH for
around 20 minutes and when I get off and come to my first stop the idle
stays high then also.
Any ideas on how to elminiate this problem?
First step, clean the idle air control. Use throttle body cleaner.
Disconnect the MAF connector, and the throttle body to air cleaner tube
at throttle body
Look down the throat and see the port to the IAC, just in front of
Start car and spray throttle body cleaner into the port, backing off if
engine starts to die.. also around throttle plate.
Dont go crazy, it doesnt have to be shiny.. if that's what you want, tear
the assenmbly down to clean it.
If that doesnt do it, move on to other things.
Also check the vacuum modulator on trans (if it has one) esp if you note
hard shifting occasionally
A good source of info;
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