My daughter's '92 F-150, 5.0, E4OD, 4x4 has developed a problem recently... It is kind of hard starting (she has to crank it for a few seconds- not necessarily a big issue after 213,xxx miles), then it will hit the high idle, which seems to be too high. After it warms up, intermittently, it will begin loping or surging while at idle. Other than that, it seems to drive ok. It does have headers, so I am guessing the EGR is blocked off? I looked around for vacuum leaks, and though I did find an HVAC line was crap, after fixing it, the problem persists. I was leaning towards the Fuel Pressure Regulator, as I had an old Bronco with similar symptoms, and the FPR turned out to be the culprit. Any other ideas? Thanks.

 

Any codes? A vacuum leak large enough to cause those symptoms should set a lean or rich code.

If there's no codes, and you find nothing else wrong, I'd suggest cleaning or replacing the IAC, and checking the TPS for proper operation.

 

Agreed on pulling codes. A rolling or unstable idle is usually from a bad TPS or IAC as previously mentioned. There's probably a dead spot in the TPS after all these years, happened to mine over the winter.

 

No CEL, but that's not to say the bulb is not out.... It may well be. I'll take it to Autozone tomorrow and see if I can pull anything. My wife works there, so maybe I can just have her do it. I had her bring home a new Fuel Pressure Regulator yesterday. I'll put it in too. It was cheap and easy, so we'll see if that does anything. Thanks for the responses. I'll try the TPS and then IAC if nothing else works.

 

Be prepared for them to tell you they can't read codes, because it's not OBD2.

Fuel Injection Technical Library

Check there for instructions on how to read codes, and for code charts. Yours will be 3 digit codes. Super easy, and all you need is a paper clip or jumper wire.

 

I also have a 93 F150 did the same thing. What I found no rocket science,
and no one even thinks to look is > take a look at that tomato soup can.
two nuts under the plastic fender and the bottom all rust pin holes loosing
all kinds of vacuum. I had to buy a new Pineapple juice sorry I didnt drink none
Its appears to be exact. Ice pick the center drain juice, cut circle install the
plastic vac line insert I had to make a bracket, solder bracket, done, runs like
a champ. Modern crap depends on vac. Theory, drill a hole in your throat,
and try and breath through your nose, thats what is happening.

 

Or you could get a plastic replacement from a junkyard that came on later model trucks...

 

The Autozone employees are generally clueless about how to use the EECIV reader, but they have one. They all know me, so they let me use it in the parking lot. I've done it before on my old '95 F-250 and some friends' vehicles.

 

Awesome then!

 

Well, I replaced the FPR, and now the truck will not idle on its own at all. It starts then dies. I can keep it running with the pedal, and have gotten it to idle a little while on its own a couple times. I don't think I hit any vacuum lines or electrical connections while under the hood, but who knows... Now the CEL is on, so I am going to read the codes in a bit. Will post what I find.

 

Just pulled a couple codes... 123 and 327. Looks like TPS and EVP are bad, though could be vacuumm leaks.

 

Time to get the ol' dvom out...

If the EGR was indeed removed when the headers were installed, how was the solenoid dealt with?

 

Replaced the TPS and EVP, as well as cleaned up the throttle body and IAC while it was off. Also noticed that someone had installed one of those "throttle body spacers" with the screw shaped insides... Most likely of not benefit, but I cleaned it and put it back in anyway. Truck runs great now. No surging. Seems to have more crisp throttle response... Although, now I am hearing a light clunk from the front end while driving at lower speeds. I am thinking it is one of the u-joints in the front axle, or possibly I did not tighten the spindle nuts properly when we did the brakes the other day... But that is for another thread.

 

Damnit. Took care of the front end noise, and the truck started the surge at idle again... We gave it a tune up yesterday- plugs, wires, cap, rotor. Still an intermittent surge at idle. Seems to occur on either the front or rear tank, too. No CEL, and I have not checked for any other KOER codes yet. Will do tomorrow. Also, I reused the throttle body base gaskets, as they looked pretty good (an thicker than stock) when I pulled them off. I am guessing they could be leaking, and causing the issue. Will check for vacuum leaks tomorrow too, if no codes found. Any other ideas? Other than the intermittent surge at idle, it runs great.

 

Did you end up fixing this? My truck does the exact same thing. tps replaced 40,000 miles EVR solenoid replace, newer used IAC.