99.5 truck surging at cruise rpm?

[hairba11]

I have a 99.5 f350 6 speed, 2wd 180k miles. stock everything.
while cruising at constant speed i get a surging, not quite all the way to bucking, but in lower gears you can really feel it. I can't drive in 2nd gear without de-clutching to keep the thing from breaking an axle or giving me whiplash.
this happens between 1400 and 2200 rpm in any gear while holding constant throttle. It may show up during acceleration, but is not as noticeable.
does NOT occur with cruise control turned on.
The SES light is on, and has been since i bought it. I have scanned it with everything from the $60 Autozone scanner to the $2000 snapon scanner and no codes are present, pending, or stored in history, nothing to reset, no idea why the light is on but don't feel like paying the minimum $207.95 diesel diagnostic fee at the stealership.

since it doesn't happen while cruise control is on, but does under manual control i am figuring it is something electrical. potentially throttle position sensor? a call to NAPA and there are two, one on the end of the throttle cable (for $70), and one built into the accelerator pedal (dealer only $330).

anybody here have any ideas?
shouldn't a faulty throttle or accelerator position sensor trip an error code or does it just think you are manually stomping on and off the pedal until it actually goes out of spec?
Oil has been changed at 5000 mile intervals using rotella.
Air and fuel filters changed every 15,000 miles.
any other questions please ask.

[Zaairman]

Sounds like your TPS is acting up... These trucks don't have a throttle cable, so that rules out the cheap part...

[russtwentyfour]

Napa has them here's the part number, 219093 for 40.50. I had same problem, bought one from napa but before I installed it I removed mine and cleaned with electrical parts cleaner while operating with screw driver and has worked perfect since. Put new one in glove box next to cps for back up.

[hairba11]

ok, now it that the sensor attached to the accelerator pedal?
like one of these dorman ones?
New Dorman Accelerator Pedal Position Sensor F250 Truck F350 F450 699 200 | eBay

[russtwentyfour]

Yes same one much cheaper at napa. Just unplug from harness, then unscrew the 2 torks screws (I think they are #25,s) and sensor comes right out. Should be able to change in a few minutes. But like I said earlier I took the ford sensor out turned it upside down and soaked with electrical cleaner and operated sensor at same time. That was a year ago and about 30k miles ago and it still works perfectly. Hope this all helps.

[hairba11]

sounds good, i'll give it a shot with some contact cleaner today and report back.

[maddawg89]

Thanks! I'm gonna do mine as well! Can you give mea specific location?

[russtwentyfour]

Location for the tps? It's the on the back of the accelerator pedal m

[hairba11]

Yeah, pop the big fuse panel cover off and you can look right at it sitting on the top left side of the pedal. I took pics of my progress and will get them posted in a bit.

ok. here are pics, and a huge thanks to Russtwentyfour!

uses T25 torx bit
viewed from fuse panel opening



viewed from floor under dash


there is a flat tab coming off the pedal that goes into a slot in the sensor and makes a 90 degree twist. Turning it by hand there was a sticky spot right off of 0, and flaky slippery spot at about 45 and a hard sticky spot at 75-80 degrees and it would hang up and have to be forced back down.


I filled the turnable slot with contact cleaner and twisted it back and forth for a couple of minutes with the screwdriver.




after a couple of minutes of turning it, the sticky spots went away, and there is apparently a spring return inside the sensor which actually started working again once the crud was cleaned up.
i kept turning it after dumping out the excess contact cleaner until it dried, then reinstalled it.
truck works beautifully now.
I didn't realize it but the inch of deadzone at the start of pedal travel wasn't normal and the truck actually takes off without having to floor it. Still no hot rod, but not quite as much of a dog as it used to be.

the contact cleaner i used was: LPS Micro-X fast evaporating contact cleaner which is labeled safe for plastics

[russtwentyfour]

No problem man glad I could help.