99 F250 LD 4x4 w/ 5.4l 203k miles.
Recently cleaned the IAC Valve,MAF sensor , new TPS. Truck was running
great , just wouldn't idle high enough rpms. Thus the IAC valve cleaning.
Works fine now. Although it revs to about 17 - 1800 rpms when first started. Comes down to 1200 almost immediately . Then it drops to about
700 withing 30 seconds. (Probably need to replace the IAC Valve) anyway, since I poked the giant so to speak , within the first mile or so, I've noticed that at very low rpms I can feel a slight surging. Worse at times than others. Then when the engine warms it's gone. Could the IAC
Valve cause this? Fuel filter? TPS? I've looked for a bad vacuum line to no avail. I'm also getting a insufficient egr flow code. Egr seems to be working fine. Don't know if the DPFE sensor is bad yet. CEL went out , I'm sure it will return . I know you guys can help . Thanks in advance. Sorry for the long post. Just trying to provide enough info.

 

The IAC is working because the PCM is able to control it's opening as well as the PCM is bringing the idle down to near spec at about 650 hot idle.
The surge is almost never the IAC at any throttle "well above" where the IAC normally controls airflow.
I would look to ignition/ plugs etc first then any bad hoses on the intake manifold.
The EGR system could also cause the surge by opening the EGR when it is not supposed to due to a faulty vacuum regulator.
When the EGR is operated, the ignition timeing changes, the fuel can go lean and exhaust gas is allows into the intake.
There would certainly be drivability effects felt by this action.
Don't rule out water in the gas or bad gas.
When you investigate all these items, and repair the EGR code, reboot the PCM to cause it to start from it's base program and rebuild the operating tables and get rid of any settings it was using due to any past faults.
Good luck.

 

Thanks for the info. Bad gas? That could definitly be the problem. I remember just before this started I was having one of those day's with alot of brainfarts. I went to a BP that is foreign owned,( need I say more ), not only did I screw up by going there but like a dummy I put
93 octane instead of 87. Don't know if that will effect it but water or just
plane bad gas could. 97? I guess I was thinking I was In my car. I've filled up since then at my usual place and added some amsoil fuel injector cleaner . I guess I'll wait and see if it clears up or the cel comes back on.
Then I'm going to look at the vacuum regulator and lines. EGR seems to be working correctly. Too hot to get to involved while the truck is running okay , no more than I drive it lately. I'll let you know. Thanks!

 

I noticed mine did that last winter as well. I had a knowledgable friend hook his code reader to it and no obvious codes causing the CEL to illuminate, but the EGR system lights were all blinking on his screen. He said to either wait until the CEL lights up or named off about 10 things to replace to 'see' if that would help.

But, any further help and or updates on fixes would definitely aid me in figuring out what's causing the 'surge' too.

 

Drove the truck about 65 miles yesterday . Different conditions. City, highway, and offroad 4x4. No cel yet. Beginning to think it was bad gas as
the surging continues to lessen. I'll keep updating to let you know. Might
still be something else.