rideRED484

Hi guys, new to the forum so this is my first real question on here. I have a 2000 F-150 XLT 5.4l, and I'm having some issues. When I fire it up after sitting overnight, it will idle fine until the temp starts to rise. Once the gauge gets about a quarter of the way up, it will start to surge (rpms up and down) like it has really aggressive cams in it. It does that for a minute or 2 then stops, and is good for the rest of the day. If I don't let it warm up, and just fire it up and go, it will quit running and 3, maybe 4 cylinders once the gauge gets a quarter of the way up and barely pull itself. It clears up after about 10 seconds and is fine for the rest of the day. I work at a repair shop, so I have been through just about everything on the truck. Also, it throws no codes. I have used our head gasket tester to look for combustion in the cooling system and it checked out fine. PCV valve replaced, plugs and boots done, fuel filter, Cleaned throttle body, cleaned MAF. I'm stumped. Sorry for writing a novel.

Heritage04

Have you run it on an OBD2 Scanner? I ask because my F150 although it has a 4.2L has the exact same thing you are describing. I don't have a CEL on, but I had a buddy plug his scanner in and it said Sensor bank 1 and 2 were lean, and O2 sensor code. I haven't had a chance to replace my o2 sensors since I just relocated from FL to NC and have no money while I job search... which hopefully ends soon. If you can give it a check, it could be something like that. just my .02

Hope this helps somehow.

rideRED484

Yes I have had it on an OBDII scanner. I have a check engine light on, but the code I am getting says "OBD scan diagnostic incomplete" but that's about it. One time it had a code that read bank 1 and 2 rich/lean, but that went away. The only thing I've done to the truck as far as modifications is cut the cats and muffler off, and run 3inch duals from manifolds all the way back. Me and my buds have done that to all of our F-150's with no CEL or any ill effects.

rideRED484

Also, gas mileage is still the same as when it had the full stock exhaust on it

rideRED484

Bump

rideRED484

Bump, any ideas? Suggestions?

Warspite

I'm chasing an idle ghost myself. No sputtering, but higher idle and tranny shift points than need be. I cleaned the MAF, throttle body, replaced PCV valve, and no improvement. Next thing to check is the IAC valve (do NOT clean this with Carb cleaner - it's too strong). Are all of your vacuum hoses in good condition? I'm following the steps on the following link:
http://www.2carpros.com/articles/engine-idles-too-high

There's a number of videos on YouTube on vacuum leak. One of them has an improvised smoke test (I smoke cigars, so I might try this if all else fails) to visualize where the leak is. I occasionally get the P071 and P074 (lean mixture, both banks) codes.

rideRED484

Yes I have checked for vacuum leaks, we have a pressurizing smoke tester at the shop, and I found no leaks with that, with both cold and warm engine. I never thought about the IAC because it idles right at 750 rpm smoothly, except when it goes into one of its fits.

Warspite

With a scan tool, I'm reading 700-715 RPM, but cluster tach says 1100. Disconnecting the electric plug drops the idle to about 680. Mine may be totally shot, but yours may be sticking, or something. If you passed the smoke test, then at least it's not the intake manifold gasket or an injector O-ring. If it's fuel delivery or pressure, could it be a fuel rail (if you're losing cylinders on one side?). Even with the leak, my 4.6 idles smooth with no misfires. Different ghosts, I presume.

rideRED484

I'm going to put a fuel pressure gauge on it and see if there is a change when it does start acting up, never thought of that.