04 Yukon Denali self accelerates briefly at prolonged idle

[Ken Taylor]

Im stumped! A little of my background, I'm the original owner. I've done all maintenance on this vehicle according to the maintenance manual schedules and beyond. I'm a plumber (40 yrs) by trade, not a professionally trained mechanic. But i can do my fair share and beyond at fixing things with the help of Utube, etc . . To my problem, About a year ago I was in a fast food drive thru line that wasnt moving so fast and while my foot was on the brake i got a lunge, self acceleration. At first I thought maybe my foot partly touched the gas pedal but no, I didnt. K, that was weird. A couple months go by and it happened again in heavy traffic at a long stop light. Another few months go by and it happened again, this time it died afterwards. Started right back up, no problem again. Then my fuel pump went out. Located in the tank of course so I replaced the pump and thought I better go ahead and replace plugs, wires, radiator, hoses, battery, got a new K&M air supply & filter etc . . The cars 14 yrs old, 101k never had problems with the vehicle but thought I'd just upgrade just cause. Using all AC Delco when I could. Anyways, this self acceleration is happening more frequently now. I took it to a shop nearby, left it over a day and mechanic said it never acted up. He didnt even charge me which was kinda weird, but cool of them. Driving home it happened again, a block from the shop that said they couldnt find a problem. Couple days go by I took it to another shop, left it there for 3 days. They said it acted up once but couldnt find the problem. I went ahead and changed throttle body, throttle sensor, cleaned MAF (again), order a bunch of other sensors, etc . . So here I am, HELP! Really appreciate any advice on this one. I have a feeling it's the computer but not sure

 

[Doubeleive]

could maybe be the throttle position sensor or accelerator position sensor if not then maybe a short in the harness

 

[91RS]

The throttle body usually fixes this but I would want to do is make sure the PCM has the latest calibration in it, this will be dealer only. I usually update the PCM with the new throttle body. If you replaced the throttle body with a GM one (not aftermarket) and the problem still happens with the PCM updated, it would be time to run new wires and connectors from the throttle body to the TAC module.

 

[Ken Taylor]

could maybe be the throttle position sensor or accelerator position sensor if not then maybe a short in the harness

Hello Doubelieve and Happy Thanksgiving. I changed out the TPS when I bought a new throttle body, it came with a new one attached. I figured I might as well take care of both pieces and cost wise it made sense seeing that the TPS cost about half anyways (AC Delco from Amazon $155). Btw, I'm glad I did change out the trottle body because all these years of me thinking I'm doing a good job of cleaning that thing, I really wasnt. I've always cleaned it still installed with tooth brush etc. When I pulled that throttle body off that intake area was filthy! Grimmy/sootlike buildup over 15 yrs took 7 shop towels in that one little area to finally clean properly all the while being careful not to knock any of that stuff in the engine.
Put in all back together with the new one, cranked it up and the thing purred like it was new again. I just let it purr along. Cracked a cold bud light, high fived the old lady and we were sitting on cloud nine, finally fixed the problem!
20 minutes later it self accelerated and died. Lmfao! Back to square one.
Shut the hood and mowed the yard. Came back a couple hrs later and cranked her up again, smooth purr. Took her for a spin and a couple hundred yards it coughed, spit and right back to smooth. I thought maybe computer relearning so I was hoping I'd still be fixed.
Ran great for a week then sitting in traffic, self acceleration again. When its starts doing that I put it in neutral a feather the gas a bit until it calms down As long as its driving and not sitting it runs fine.

As far as the pedal sensor I cant find a ac delco without buying the whole paddle assembly, $250 or so. Dormain has one for about $25. Hate to use any other off market brand but in this case I'll get it a shot. Thank you for your input

 

[Ken Taylor]

The throttle body usually fixes this but I would want to do is make sure the PCM has the latest calibration in it, this will be dealer only. I usually update the PCM with the new throttle body. If you replaced the throttle body with a GM one (not aftermarket) and the problem still happens with the PCM updated, it would be time to run new wires and connectors from the throttle body to the TAC module.

91RS Happy Thankgiving and thank you for your input!!
I cringe when I think about taking this thing to the dealer. But you're right it's time for that. I just got a new MAF and will be replacing this piece. I'll also be replacing the pedal sensor with a Dorman (unfortunately) to see if any of these pieces help all the while knowing that Dorman isn't going to be a permanent piece.
The wiring replacement is now on my list but probably after seeing what the dealer tells me.
Thank you for your input. I really appreciate you!

 

[Mechanic421]

A good shop/scanner should catch the glitch while data logging.

 

[Ken Taylor]

A good shop/scanner should catch the glitch while data logging.

Hello 421. That's what I think too. Although the 2 shops I took this vehicle to have excellent reviews I think they already have plenty of business to not have this headache atm. I havent found the right shop yet

 

[Mechanic421]

Were are you located?

 

[Ken Taylor]

Were are you located?

Fort Walton Beach, Fl
Northwest Florida. Where u at?

 

[Mechanic421]

Just moved to North Carolina from south east Florida.