Truck accelerates on its own

[Rgbraun1]

1999 Silverado 5.3 vin T.

Hello, I'm new to the forum. Here's my issue with my truck: I felt the slightest surge while cruising...I planned to do my ujoints so while replacing the U-joints and carrier bearing I decided to clean the throttle body and ended up replacing the IAC. On test drive I got a violent shake so I pulled the driveshaft and 180 degree turned the rear shaft on the slip yoke. The shudder went away but i noticed the the truck accelerating on its own, i put in gear and tap the gas and can take my foot off the gas and it will slowly accelerate through all the gears and gain speed. I put on a new TPS. Drove the truck 200 miles home (did all this work at my dads garage) and got a shake bewtween 35-45 mph and the accelerates on its own. Started getting different codes so I replaced EGR, MAP, MAF, throttle body gasket, engine temp sensor, plugs and wires, PCV and PCV grommet. I also replaced the connectors for the TPS and IAC. I finally took it to dealership and it took them 2 days and 3 techs to tell me it was intake manifold gaskets. So I replaced the gaskets (and the knock sensors and harness) but it still accelerates on its own. So, as it sits. My truck still accelerates on its own and it shakes at 35-45 mph. Is the shake from an imbalanced driveshaft? Or a bad torque converter? Can a bad torque converter cause the accelerates on its own problem. Also, while cruising, I can take my foot off the gas and the truck will maintain its speed. I have tried removing the cruise control fuse to be sure it wasn't faulty. Hoping someone can help. Thanks.

[GMCustomerService]

Hi Rgbraun1,

 

We are sorry to hear of the concern experiencing with your truck and understand how worrisome something like this can be. If you would like for us to look into this further, and reach out to your dealership, please let us know in a private message! Be sure to include your VIN, current mileage, contact information and preferred dealership. Hope to hear from you soon!

Best,

 

Bret B.

GM Customer Care

Hi Rgbraun1,

 

We are sorry to hear of the concern experiencing with your truck and understand how worrisome something like this can be. If you would like for us to look into this further, and reach out to your dealership, please let us know in a private message! Be sure to include your VIN, current mileage, contact information and preferred dealership. Hope to hear from you soon!

Best,

 

Bret B.

GM Customer Care

[Heavy 5.7]

Have you already tried using smoke/propane/carb cleaner to locate a leak? (this would have confirmed an actual intake manifold gasket leak)

I'll assume the throttle valve was removed for cleaning, did you use a new identical gasket when reinstalling?

Did you inspect the throttle shaft for binding and excessive play?

Are the cables leading to the throttle body correctly routed and not binding?

When the vehicle is accelerating "on it's own" can you lift the accelerator pedal with your foot and slow it down?

[ttommytucker]

Lots of $ thrown at parts. Maybe testing many of those parts first with a simple multimeter or other testing methods would've saved you alot of $ instead of finding out that they weren't bad after all. I'm not bashing the owner, but you hear about people and mechanics just throwing parts on a vehicle without ever testing the parts first. I do hope you find your problem though.

[Jsdirt]

^^^ Where were you guys when my truck was new? Spent more time getting warranty repairs in the service bay the first 36k miles than I did actually using the damn thing.

 

 

Anyway, to the OP:

 

Wow - you BLASTED that thing with the parts cannon at close range! I feel bad for your wallet ...

 

That shake your feeling could be the result of a dead or intermittent miss rather than any driveline vibration. Hindsight is always 20/20, but you should've stopped at the driveshaft. Got to diagnose these things - don't just guess! Plenty of Youtube vids out there about specific problems or codes that may be present. You could've got yourself a nice set of tools for what you've spent on parts ... and parts/labor at the dealer.

 

Why on earth would you go to a dealer with a '99 model year??? You're just asking for a depleted bank account. If you don't feel confident doing the repairs yourself, at least find a local, small garage that has a good reputation fixing drivability issues. Your bank account will thank me x10 ...