Starting about a month ago, and getting worse, my wife's 1989 Ford Crown Victoria (4d, AC, Auto, PB, PS, loaded), has developed a idle roll. The rpms increase, then decrease, then repeat. Sometimes this roll will take repeat approximatelya half dozen times then smooth out to a normal idle. But in most cases, the rpm will drop to an extreme low on one of the rollswhereas the engine will die out.

We encounter this problem constantly ie a cold start, or after a drive to the supermarket, grocery shop a half hour, or have breakfast at some restaurant, then restart the vehicle. The idle rpm roll occurs.

The vehicle is due for a tune up but this idle roll has never existed before and of courseI strongly expect that whatever is causing this problem will not be related to the tune up charges.

All comments that would point me in the proper direction to cure this problem first (before tuneup) will be most appreciated.

 

Pull the intake hose off and look into the throttle body bore.. There'll probably be 'black' debris collected on/around the throttle plates edge and in the bore itself where the plate close's into.. Use some throttle body cleaner,wedge the throttle open or have someone hold it open for you.. Spray the plate/bore liberally but don't flood the intake, then use a soft brush to clean both the plate and bore.. It cleans off pretty easy.. If this doesn't correct the idle roll, the next stepcould be the IAC (idle air control motor) hanging, or possibly restricted with debris or faulted..

 

Also check the Air temperature sensor. It is located in the intake on the drivers side screwed into an intake runner. It will get carboned up and give a bad reading causing the rolling.

 

Hayapower: I removed the air intake and cleaned the throttle butterfly and the intake throat.

I also removed what I think is the IAC valve from the intake body and carefullyinspected and cleaned it. This is a small three wire electrical device which appears to be a resistor that has a movable interior that is turned by the throttle butterfly. I did not use any liquids in cleaning this device.

The result is that whenstarting a "cold" engine, the engine idles normally. However, after a short run over to the supermarket or some other store, then after a shopping period of about 30 or 45 minutes, then restarting the vehicle's "warm"engine, the rolling, surging, loping idle effect returns.

Way2old: I'll see if I can find the air temperture sensor you mention.

 

If I remember correctly, it is a 2 wire connector between number 5 and 6 cylinders. When it is removed it will have a little bulb in the center of the sensor. Probably red in color.