1990 f150 fast idle.

Could someone please shed som light on why after my truck warms up the fast idle will engage for no reason? How do I fix this? :banghead:

Welcome to the forum. What engine?

Could someone please shed som light on why after my truck warms up the fast idle will engage for no reason? How do I fix this? :banghead:
Please let me add my similar problem to this thread My 91 F150 econoline ltd? V8 302 has started to rev to 3.5K rpm. If I turn it off and then start it, it will be ok for about 2 minutes. It used to rev up only during starts. It cranks up right away and will die quickly after if you don't hold the rpm up.
Thanks for any help

I would check the Idle air control (http://www1.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/0a/2c/65/0900823d800a2c65.jsp) valve first.

Good luck and let us know.

Hello, thanks for replying. Here's what has happened. i changed the IAC but no fix (thankfully they let me return it). He suggested the Temp sensor since it might send info for the IAC,? I told him the engine light comes on periodically. So the codes came back with the EGR valve about 3 times, the O2 sensor, and the computor. He suggested cleaning the EGR valve. On the way home it ran pretty good; low idle, no surges, no stalling. Parked it for the night; next day started removing the EGR but could not break loose the rusted nut. put some break loose on it. While that soaks, I tried starting it. No go. it seemed very out of time or like only two cylinders were firing. What a drag!! So I did a tune up; new wires, plugs, cap rotor. This got it started but it has a serious sounding noise; like an exhaust manifold leak. When reving it, the power sounds like a missing cylinder or like the "Limp Mode" that a computer causes when it gets an error from a cylinder. i wonder if the codes can be cleared on this model.

sorry for the long wind; it just really sucks for it to go so bad over night.

Clearing the codes didn't help. This thing barely runs at all now; if at all. Would the ICM go out just like that? What kind of special wrench do you need to take it off?

Clearing the codes didn't help. This thing barely runs at all now; if at all. Would the ICM go out just like that? What kind of special wrench do you need to take it off?

ICM?
What were the codes?
No more fast idle?

I'll have to remember they were 31,32,33,41,53. The ignition control module on the side of the distributor might be bad? because now the engine turns over very rough and will barely start. I haven't got it to run good enough to check the fast idle again. It sounds terrible like it's completely out of timing.

Get it running first. As many times as I have replaced plug wires I still occasionally get the crossed. I would start with double checking them and if it runs then the timing. If you still have a no start check for spark (http://www1.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/17/4f/9d/0900823d80174f9d.jsp). Here is a link for the ICM replacement (http://www1.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/17/4f/eb/0900823d80174feb.jsp). Get it running and let us know. The links below are for test procedures for the various components.

31 or 32
Both
EVP sensor out of range
EGR (http://www1.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/17/55/f0/0900823d801755f0.jsp) is sticking or EVP (http://www1.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/17/57/98/0900823d80175798.jsp) is bad.

33
KOER
EVP sensor indicates EGR is not opening properly
EGR is bad, EVP is bad, and/or there is a vacuum leak

41
KOEO
Right EGO2 failure
EGO2 is bad, not connected, or missing.

KOER
EG O2 indicates right bank lean
EG O2 (http://www1.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/17/56/a8/0900823d801756a8.jsp) is going bad, missing, or fuel pressure regulator is set too low.
Clean the maff and look for vacuum leaks also.

53
KOEO
TP sensor out of range
TP sensor (http://www1.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/17/57/61/0900823d80175761.jsp) is stuck/sticking or just plain bad. It would be a good idea to
get a replacement.