Starts accelerating on its own!!

[A-Mac]

2007 Tahoe, LT2, 165k.

On a recent trip to LA, when coming to a stop I noticed that my Tahoe seemed to lurch forward. It was as if I was pumping the throttle. My foot was either on no pedals or on the brake. The tachometer would jump up to about 2500 RPMs. At the same time the temp gauge would drop all the way down. Just to prevent myself from driving into the car in front of me. I had to say really step on the brakes.

It only seems to do this, when I’m coming to a stop. And generally it’ll happen whether or not I’m touching the brake. Really strange behavior.

It did throw a P0118 (engine temp control sensor) code, but that cleared itself. It also flashed a “Engine Hot. Turn off A/C” message as well.

It’s getting dangerous and my mechanic is a little perplexed with the problem. Any ideas?

 

[swathdiver]

Check for vacuum leaks, check the condition and operation of the throttle body and Mass Airflow Sensor. I've had bad MAFs do that to different cars over the years. You'll need to hook the motor up to a scan tool and see if those sensors and such are within spec even if they are not throwing codes.

 

[Doubeleive]

I would be checking or replacing the throttle body, throttle sensor on the gas pedal, anything in between (harness), there not expensive parts at least not in my opinion. intermittent problems suck.

 

[Isaiah W]

Kind of sounds like it's trying to engine brake? Do you have tow/haul turned on at all?

 

[PG01]

Kind of sounds like it's trying to engine brake? Do you have tow/haul turned on at all?

Wasnt an option in 07, 13 was first year for grade braking or ‘engine brake’ and it cones on in Tow/haul or not.

 

[Isaiah W]

My mom's '11 has engine braking in tow/haul mode...

 

[Doubeleive]

Wasnt an option in 07, 13 was first year for grade braking or ‘engine brake’ and it cones on in Tow/haul or not.

2013 is when it became standard in non-tow mode, my 2012 has it when in tow mode, if you choose the shifter button in tow mode it disables the grade brake, at any rate I don't think it's the cause of the problem being experienced, but stranger things have probably happened.

 

[PG01]

Well, blah, blah, blah, blah and blah.....mine does it all the time.....

 

[swathdiver]

Cruise Grade Braking, Normal Mode was introduced in 2012. Powertrain Grade Braking, Normal Mode was introduced in 2013. Hill Start Assist was introduced in 2012.

I've been wondering if these features can be programmed into older trucks???

 

[A-Mac]

Mechanic found that the motor mounts need to be replaced. There was an exposed screw that was hitting the wire harness and they suspect it was causing some electrical misbehavior. They capped the screw and added some protection to the wire harness. So far, so good.