First off Hello to all. I am new here and found this site looking for someone that might be able to help me with this problem.

I am having a problem with my '92 F150 that shows itself two ways. First off whenever you are traveling at speed and have to decelerate i.e. someone pulls out in front of you, when you go to accelerate it stumbles. The other thing is that sitting at idle it goes from running smooth to missfiring then back to smooth.

Now what I have done so far. This engine has ticking lifters on start-up so I started with a compression check, which was fine. Then I checked out the fuel pump with a static and running pressure check, verified that the regulator was working. Then I went through the secondary ignition wiring, cap and rotor. Then I cleaned the throttle body, replaced the PCV valve and verified that the system was flowing. Then I checked all the vacuum lines and fittings and replaced a couple bad fittings. Next I did a self test and a running self test. It set codes for the IAC and low flow on the EGR valve. So I replaced the IAC and cleaned the EGR valve and tested the EVP sensor. They checked out. Also checked the MAP sensor along with the IAT sensor. Both were ok. Next I checked out the solenoids, found that the EGR vacuum solenoid was bad so I changed it and verified that the vacuum solenoids for the Thermactor valve were ok. But... The first solenoid valve as you look from the radiator to the firewall was holding vacuum when I went to take off the vacuum lines? After testing, the valve bled off properly.

Right now as it stands, after replacing the IAC the truck revs up on start up but after warming up settles out to a normal curb idle. I have been told that this is the EEC-IV version of a "fast idle cam" but it seems a little too fast. However, the stumble and missfire are still the same.

What else can I check out? After each round that I have done I have cleared the codes. Anybody got any ideas as to what the problem might be?

Thanks in advance.

 

Do you have the juice can vacuum resovoir on the passenger inner fender? If so take it off and look for obvious leaks on the bottom.

 

Ok Conan, will do. Anything else? Anybody?

 

Ok just an update. Since changing the IAC, whenever the truck is cold and I start it up the engine will rev up really high for about 2 minutes then slow down. It then surges in Park but once I put it in gear and its warm it idles fine. Anybody know what is causing this?