Auto-acceleration

[bonnevilleCyborg]

Hello Everyone,
I have a '94 Pontiac Bonneville. Lately, I have been noticing that the engine seems to stay under power when my foot is off of the accelerator and on the brake. Yesterday I was in traffic with my foot on the brake and I noticed the brake "grabbing" harder than usual as if the braking system was under power. I then took my foot off the brake and my car jumped instead of the usual creep it usually does. When the light turned green I didn't put my foot on the accelerator but simply took my foot off the brake. In doing so my car accelerated up to 20 mph. Noting all of this I pulled over and put the engine in park where it revved up to 4,000 rpms with once again, my foot off of the accelerator.

I was wondering if anyone knew of anything that would cause a cars engine to remain under power even with the foot off of the accelerator.


Any help is greatly appreciated.

[mylittleblackbird]

Is your butterfly closing at the throttle body?

[bonnevilleCyborg]

I don't even know what a butterfly is

[nos4blood70]

There's a valve in your throttle body that opens when you press the accelerator pedal. If you have a severely gummed up throttle body, your valve could be sticking, thus causing your weird acceleration.

[mylittleblackbird]

Hang on.... I'll find a picture.



Okay, that part inside the little red box is your throttle body. On the back side of it, between the throttle body and the firewall is the cable system for actuating the throttle body. With the car *OFF*, rotate the part that the cable connects to. You should only be able to rotate it about 90 degrees. You can rotate it one way, and a spring will resist you. This is your throttle return. It should return so that a portion of that throttle cam rests against the throttle stop. If it does not return to the throttle stop, you most likely have a broken return spring or a gummed up throttle body.

If it does not return to the throttle stop(closed), pull on the steel cable that goes to the throttle body cam. If it returns to the throttle stop, your cable is catching on something(not likely to happen, but possible). If it does not return by pulling the cable out a little bit, try rotating it to the throttle stop by hand. It should move freely to the closed position. If there is resistance, you most likely have a gummed up throttle body. After it goes to the closed position, see how easily it will open again. If there is very little/no resistance, you have most likely broken the return spring.

I hope this is of help to you.



This isn't the same throttle body as what is on your car, but it's similar enough. On the left side, that black piece is the throttle cam. That is what you're looking for to do what I described above.

[bonnevilleCyborg]

Thanks fellas, I'll get into checking this sometime this week. And I've rolled over 300K miles yesterday, so I want to do anything within reason to get it to 400K.

[bad.moshi]

Sounds like a funny TB. I was noticing weird acceleration or revving issues when my throttle position sensor was going kaput

[88bonnsse]

i have a 95 sle with known computer issues for this year. my car did the same exact symptoms as you described and i was stumped. looked over everything including the butterfly.

turned out my pcm ( computer ) was going bad and was randomly accelerating on its own. even with my foot on the brake at a light.

not sure if the 94 bonnevilles are known for computer issues also. just putting my experience out there.

[bonnevilleCyborg]

As a computer programmer, I hate when people find the solution and don't post the answer in the forums. Anyway, I got the fuel line treatment cleaner while at the oil change place. Once that happened, it never auto-accelerated again. I assume that something was getting stuck with debris or dirt/grease and the treatment fixed it.

[J Wikoff]

My guess is your idle air control valve was stuck open. It is in a passage that bypasses the throttle body and it what allows the car to idle when you don't have your foot on the gas pedal and the throttle plate is closed. It could have been sitting wide open. I'd clean it.

[Bob Dillon]

I'd clean it.

A shot of WD40 on the shaft end and the throttle cable might work, too. It sounds like a sticking throttle cable to me.