This thing is killing me. We've got a 1999 F250 with the 5.4, 155,XXX miles. A few weeks ago, it started surging at idle after warming up. When you come to a stop, it runs fine but the longer you sit there, the worse the surging gets.

No CEL, hooked it up to a SnapOn scanner, ran diagnostics, no codes, no faults. Checked for vacuum leaks, don't find any (sprayed carb cleaner around gaskets areas, vacuum lines and no change in idle). I will fluctuate between 650-800 rpm. Doesn't matter if in neutral or park or drive.

Replaced the MAF sensor as it was original after cleaning and no change(scan tool did say MAF was reading about 1.0). Next thought process was TPS as during testing, I could watch the analog volt meter sweep from .6v-1v with key on engine off. So thought a bad TPS. Plugged in new TPS (not hooked to butterfly valve so just checking throttle closed) and no change in RPM, still surges. Old TPS was steady increase as throttle was opened with WOT reading 5v, didn't see any dead spots.

I've heard that the PCV line will develop a crack, but I've sprayed WD-40 and carb cleaner as best as I can around the back of the throttle body and it didn't change.

Fuel mileage is horrible. We have "normal" power and no miss or hesitation driving around town or on the interstate so I haven't looked into COPs, plugs or injectors.

 

IACV behind the throttle body. Try running some seafoam through the brake booster hose first and see if that helps. If it clears and comes back change the IACV.

 

I've already removed and cleaned the IAC and ran Seafoam through the vacuum line off the brake booster. That was my first thought.

 

So I took the PCV line and elbows off and replaced with 3/4" heater hose and a new PCV valve. Same issue. I've already cleaned the IAC. I'm really stuck, any advice? I really don't want to clean the throttle body just for fun.

EGR is fine as you can watch the piston move up and down while running.

 

Subscribing because my expedition does the same thing. It will be idling fine at a red light and then all of a sudden surge forward and you have to hold the brake. Cleaned the stuff mentioned here and no change.

 

If it has the same plastic intake that the 150's have I have seen the intake crack and cause this.

 

Ok, found the culprit and had time to work on it. It was a stuck EGR valve. If you want to check, without pulling, you should be able to prove the top wire on the DPFE. At idle the voltage should be down around zero as the DPFE measure exhaust gas flow through the EGR. Took the old one off and it rattled and you could blow through it(bad). New one on and idles great again.