93 g20 350 excessive engine speed

[bfktwb4]

Hey guys need some help. The wife was driving the van the other day and the engine started to suddenly accelerate. Think runaway toyota type runaway. She had to put it in nuetral and have it towed home. The engine acts as if you have the gas pedal half way down. You can hit the gas and the engine speed goes up but it will not drop to normal idle speed. Although I haven't put an RMP gage on it, think 3000rmp without your foot on the gas.
It is throwing a 37 code (TCC brake switch circuit error) which I think is unrelated (the ABS light has been comming on intermittantly for a few years now)
Any help in troubleshooting would be appreciated.

[MT-2500]

Originally Posted by bfktwb4

Hey guys need some help. The wife was driving the van the other day and the engine started to suddenly accelerate. Think runaway toyota type runaway. She had to put it in nuetral and have it towed home. The engine acts as if you have the gas pedal half way down. You can hit the gas and the engine speed goes up but it will not drop to normal idle speed. Although I haven't put an RMP gage on it, think 3000rmp without your foot on the gas.
It is throwing a 37 code (TCC brake switch circuit error) which I think is unrelated (the ABS light has been comming on intermittantly for a few years now)
Any help in troubleshooting would be appreciated.

Check throttle body butterflies for closing and gas linkage not sticking open and IAC motor is not car-boned up or stuck open.

Next step is check for vacuum leaks

If throttle body injection.
Base gaskets are a known and leading cause of fast idle.
So your next step.
Is to remove the throttle body and replace the base gasket.

Let us know hoow it goes

[bfktwb4]

Thanks for the reply. I got a chance to look at it today for the first time. The gas pedal cable that hooks to the throttle body (butterfly?) is ok. At this same point there is a rod linkage that is connected to a diaphram of some sort. The rod fell off the diaphram (connector is broken) and hooked itself onto a bracket. This prevented the gas pedal cable to return to it's origional (idle position). My problem now is the diaphram needs to be replaced but I dont know what it is called. I cannot locate it online nor in my Haynes manual. It has an electrical connector on it and two vacumn lines. It is mounted on a bracket to the drivers side rear of the throttle body. Wish I could send a picture but I don't have a camera.

[MT-2500]

Originally Posted by bfktwb4

Thanks for the reply. I got a chance to look at it today for the first time. The gas pedal cable that hooks to the throttle body (butterfly?) is ok. At this same point there is a rod linkage that is connected to a diaphram of some sort. The rod fell off the diaphram (connector is broken) and hooked itself onto a bracket. This prevented the gas pedal cable to return to it's origional (idle position). My problem now is the diaphram needs to be replaced but I dont know what it is called. I cannot locate it online nor in my Haynes manual. It has an electrical connector on it and two vacumn lines. It is mounted on a bracket to the drivers side rear of the throttle body. Wish I could send a picture but I don't have a camera.

Sounds like cruise control diaphragm.
Do you want cruise working?

Bone yard or if factory OEM cruise the chev dealer may be able to get it for you.

[bfktwb4]

BINGO!!! Thanks MT. I looked up cruise control diaphram on autozone website and the picture is exact! Will just disconnect it for now until i can get one, so I can drive the vehicle. Thanks 100% Great forum!

[MT-2500]

Originally Posted by bfktwb4

BINGO!!! Thanks MT. I looked up cruise control diaphram on autozone website and the picture is exact! Will just disconnect it for now until i can get one, so I can drive the vehicle. Thanks 100% Great forum!

You are welcome and thanks for posting back hat you found.
Good Luck