My brother's truck (07 F-250 Super duty 2wd auto 80,000 on the clock) surges under heavy throttle. From about 50% on up it pings, bucks and surges a little. It feels stroner when you let off of the pedal a little, like there's more acceleration. Does anyone have any ideas on what could be causing this?

A little background info. He has had the surging under load issure for a while now. It didn't happen when the truck was new either. His battery died the other day so he went out to get a new one. Well when he installed it, he was having a problem with it idling so low that it was dying and throwing a code. Got it scanned at the local auto-zone (twice because the first time the lady said that the wiring was bad and it wouldn't read the codes) and it came back with the code P0506 idle control system RPM low. Well upon doing some research I found out a lot about the fly by wire system so this is all new to me.

The first thing that I did was replace to try to fix the idle problem was all 4 of the o2 sensors. He had a code issue with one before and we never changed it. I also remember changing the TPS a while back with no change in surging then. Changing the o2 sensors didn't seem to do a thing to help out the idle problem so back to the computer for more research. I know that he has a K&N air filter and I know that they have been known to get oil on the MAF and make it not run right. I took that out and cleaned it with MAF cleaner but when I re-installed it, the problem got worse. Now it wouldn't stay running at all. I was thinking maybe TPS or the throttle control motor. Back to doing more research yet again. I came across a thread about cleaning the gunk buildup out of the bottom of the throttle body so I took that off. There wasn't much there at all but I cleaned it all away anyways. Put it back together and the truck fired up and ran like a dream. It's idling and accelerating better (from low speed) than it has for the past year. This didn't fix the surging problem, it's still there under load so i'm trying to tackle that now.

A few questions on my mind. What would cause all that junk to accumulate under the throttle body? What other issues would cause the truck to surge? Sometimes, when your on the throttle pretty good, it will catch and speed up like it's supposed to but mostly it doesn't. I've seen suggestions about fuel pressure, does anyone know what the pressure reading is supposed to be? I'm going to change the spark plugs, fuel filter and put another Motorcraft paper filter in it and see if that helps any but I won't be able to for a couple of days. I know that the fuel filter isn't that old but it's worth a shot. Does anyone else have any other ideas on what it might be? Thanks in advance!

I also posted this in the Moudlar V8 (4.6L, 5.4L) forum also to see if I can get any hits there.

 

Let the other forums answer it then!

 

Lol. I posted it there a few hours ago and got noting so far. Just feeling out for as much knowledge as I can get as i've never worked on something this new and thought it might be a common problem.

 

Bump bump! Anyone?

 

Transmission? In my head, surging under load sounds like a slipping tranny.

 

I wouldn't think that it was the tranny because the engine is pinging also. The surging is too erratic and the trans feels like it's coupled to the engine during the surging pretty good. You can physically feel and hear it in the engine while it surges.

Thank you for the input though.

 

truck has same symptoms as above accept way worse if i floor it on the interstate and get truck up to about 85 motor feels like its shaking and coming apart if i take my foot of gas and coast down to about 40 it will stop shaking and run fine and run fine everytime this happens it throws code for sensor lean bank 2 i have changed all 02 sensors and all drive by wire componets truck is a 2004 ford f150 roush tejon with 189k and counting