Can anyone help me out?My 1989 F150 V8 302 when either cold or hot modulates from 500 rpm up to 1500rpm continually and back down to 500 rpm when the truck is at a stop.When moving everything seems ok.

Thanks Robert

 

First I would remove and clean your IAC valve (idle air control). If that dos not solve it pull your codes and see what you have.

 

mine did the same thing
put a new map sensor on it and vuala
i also cleaned the aic throttle body and everything else i could think of

 

What exactly is the idle air control and where is it located, my dads 1990 f250 with a 302 started doing this again. It happened a few years ago, but a garage fixed it, i would like to try to fix it myself, thanks

 

On the manifold, by the throttle body. It is about 3 inches long and about the diameter of a baseball bat handle, it will have a electrical connection on the end. The mounting plate is diamond shaped and has two small screws holding it on. It regulates air to the throttle body, more when cold and less when warm, they get carboned up and stick pretty regularly. I would try cleaning it with carb and choke cleaner first, if no luck a new one costs about 55 dollars.
T. Roberts
UFD Local 1147

 

Fixed the problem by cleaning the Throttle position sensor(TPS) mounted on the side of the throttle body.I took it apart and used carb cleaner on it. According to the manual for a 1989 ford F150 the Idle speed control valve is a throttle air by-pass valve is a solenoid operated valve controlled by the ECA module (computer) The valve allows air to by pass around throttle plates to control cold engine fast idle,no touch start,dashpot,overtemperature idle boost, and engine idle correction. This is not the TPS sensor.

 

In my manual they call what you all are describing the air bypass valve. Is this what you are talking about because I am very intersted.

 

As I mentioned before the TPS is the Throttle position sensor and
and the other is the Idle speed control by-pass air valve. These are
two different things. My problem was a dirty or erratic Tps sensor not
a Isc control by-pass valve.

 

[QUOTE=rrwitt1]Can anyone help me out?My 1989 F150 V8 302 when either cold or hot modulates from 500 rpm up to 1500rpm continually and back down to 500 rpm when the truck is at a stop.When moving everything seems ok.

I have the same truck and also had the same problem.I changed the idle control valve on side of throttle body.It solved the problem.