Hi,
My 89 F150 has what appears to be a fuel surge issue. Upon cold start, it races, almost dies, races, almost dies... until warmed up. Until recently, it ran fine once warmed up. Now, I'm getting a surge when driving but only some times. I bought it last year from the original owner with only 55,000 miles on it and replaced the fuel pump relay (he was taking off the ground cable when not using it to keep it from running). I'm a little stumped and would welcome some sage advise before I start replacing parts not knowing if they need replacement.
Thanks, Mike

 

Ohm the coolant temp sensor . Post results .

 

Surging idle can have many causes. Most common are sticking/faulty IAC, vacuum leak(s), faulty TPS. I would start by inspecting the IAC. If it is gummed up with carbon you can try cleaning it. If you have to replace it use a Ford/Motorcraft brand. Many of the aftermarket brands have less than stellar quality control.

 

I won't have access to a meter until later today. Will post when I have the result. Thanks.

 

I am having literally the EXACT same issue. I am thinking it's either a TPS or IAC. Did you ever figure out what was causing the problem?

 

Assuming that "to keep it from running" means the fuel pump, a common symptom of a bad ECU, ECM, PCM, computer, or whatever term you'd like to use would be the most likely suspect.

This might be of some help to you
Click this link:A9x ECM's (and same years ECM's) Failures Due to Age

Good luck on your quest.

Bob

 

had this happen once to myself a mechanic freind of mine showed me this trick so before you spend money on sensors not saying you wont need to but try this trick first take your intake hoses off spray brake clean on the butterflys take rags and clean them and the interior housing the best you can next open butter flys and clean the back side of them the best you can cured my problem instantly actually made it a routine maintence Note do not do this with motor running and i hope it helps save ya a buck or 2

 

Mine did that too. I cleaned my iac and it smoothed right out. Also put some dielectric grease on every connector I could reach

 

That would be the Throttle Position Sensor most likely.

 

I'd bet on the EGR before everything discussed above. Try pulling the quick-connector and see if that "fixes" things. Doing so may set a code, but don't worry about that right now, there's another more involved work-around that will produce the same effect but not set a code.

 

Fuel pressure regulator-

My 89 4.9 did the exact same thing.

My mechanic listened for 30 seconds, swapped the fuel pressure regulator, and now runs like a top.

 

This thread reads like seven blind men describing an elephant! I wonder if the OP is even still following it, or has he sold the truck by now!

 

Did anyone find a solution?

 

6 years later......

Good read in this thread from another forum: Random Idle Surge When Warmed Up - Ford Bronco Forum


I have stated many times the most common cause(s) of a rolling idle are:

Sticking/Faulty IAC
Vacuum leak(s)
Worn throttlebody
bad TPS
sticking throttle cable


In the thread I posted the OP had almost every single one of those that all contributed to the rolling idle issue.