1993 40th Anniversary Safety Issue (need help)

[tideman7]

My wife was driving the car and the rpm ran up on it's own and almost killed her in traffic. With luck she got the vehicle stopped in the middle of a intersection. After the 911 call and the towing to the dealer in LaGrange, GA the car now starts normal in every way. She had restarted it in the intersection earlier but the engine still reved up uncontrollable. The dealer is now guessing and looking at the speed control module adjuster. I am afraid he is just guessing needing to do something about a safety issue. Ofcourse the part is now not available. Has anyone had a similar situation with this model? Right now any help is appreciated. Thanks.

 

[XLR8]

Scary situation! I'm glad to hear your wife wasn't injured!

I can't offer suggestions related to the technical issue, but I can give your thread a bump to bring it back to the top of the heap. Stand-by because we've got some great tech minded folks here and I'm sure they'll chime in soon with some ideas and suggestions for you. I'll also try to edit this thread to tag it "IMPORTANT".

Good luck with your search for the cause. . . and keep us in the loop with progress.
Who knows, you may save someone else from the same occurrence with a more tragic ending.

Jane Ann

 

[93Rubie]

Is the car a auto or manual?

Check the throttle return spring for proper snap back. Should not be broken or damaged in any way.
Check the pedal, all cables from pedal to ASR unit to the throttle body all should move freely with no binding.
This is the first stuck throttle I've heard of on a C4 on a forum, so I don't think it is common.

The cruise control/ASR should not ever hold the throttle open. Check for ASR codes and operation.

Also, a massive intake leak could cause it to rev up, look at the vacuum lines for the brake booster especially. Check the rest out as well.

Was the RPM at redline or just high?

 

[John Robinson]

I'll throw out the TPS sensor as a possibilty. It is a pontentiometer and it's job is to tell the ECM how much throttle is open. The TPS is mounted on the end of the butterflys and when they are moved from closed to wot the voltlage increases on the ground wire. That reading is then interpreted by the ECM and it adjusts the fuel flow accordingly. So if for some reason the TPS gets stuck or shorts out and it tells the ECM it is at WOT the ECM will poor the fuel into the engine. If that happens then off course the engine will rev up. Keep looking until you are sure you have it solved and please keep us informed. One thing is for sure it is either a mechanical (cables etc) or an electrical issue (sensors or wiring shorting) Unless the ECM is being told it needs more fuel it won't increase the fuel needed to let the engine rev like you describe.

 

[boomdriver]

is there ANY way this could have been a floor mat issue?
I ask because I have done similar things that ended badly.

because of my big feet, the edge of my boot caught under the brake pedal and on top of the gas pedal....
The more I stomped the brake with my left foot the more that forced the gas pedal down because my rt foot was trapped on the gas. This was miliseconds...thats about how long it took me to shift out of gear (auto) and go for the key, BUT during those few mili-seconds I drove the car under the side of a new Ford p/u broadside....and had the damn truck sitting on the hood of my car. Thankfully there were no injuries..just some 'splainin to do.:ugh

I do not wear hard sole shoes in the Corvette anymore. Even if that means I have to go somewhere in my bunny slippers and put my shoes on what I arrive, thats not much inconvenience compared to scraping a p/u off the hood of my car.

 

[Hib Halverson]

Unintended acceleration which later cannot be duplicated is a very difficult problem to solve.

First, I'd definitely be looking at the possibility of a floor mat issue, mainly because the problem went away after the car was towed in.

A TPS problem might do it but if the TPS was at 100% but the throttle wasn't actually open, I don't think it would be very hard to stop the car as the engine would not run very well with the air fuel mixture way rich, nevertheless, troubleshooting the TPS is easy.

The cruise control servo might also be problematic.

The throttle cable is a possibility, too.

 

[93coupe]

unintended acceleration

I have had the problem of unintended acceleration for a couple years. At first it was minor and I thought it was my imagination. Yesterday it was more serious. I had turned on to a two lane road and was shifting from 2nd to 3rd under normal acceleration. The engine rev's just kept climbing. I pushed the clutch in and turned off the engine. The rev's had peeked at 6,000 rpms. With a restart the rev's stayed at full throttle. I opened the hood and fiddled with the throttle spring and cable. Eventually the engine worked proper and I could continue.

Has a cause been found for this problem?

 

[93Rubie]

Check the throttle return spring on the throttle body. The plates should move freely but snap shut. Check cables as well. All should move freely. Throttle pedal itself should move freely.

Also, carbon build up inside the throttle body can cause a sticky throttle. Clean it with some carb cleaner and a old tooth brush.

 

[93coupe]

clean throttle body

Thanks for the suggestion.

I've cleaned the throttle body and spring, all parts move freely. I see the cable goes into the ASR unit. The cable from the pedal goes into the ASR unit where a computer (electronics) takes over. There could be the problem. Something is taking control of the management of the throttle to open it like it has done and it is not repeatable for a demostration to anyone. I hope it is recorded in the code system to help in solving the situation.

 

[93Rubie]

Thanks for the suggestion.

I've cleaned the throttle body and spring, all parts move freely. I see the cable goes into the ASR unit. The cable from the pedal goes into the ASR unit where a computer (electronics) takes over. There could be the problem. Something is taking control of the management of the throttle to open it like it has done and it is not repeatable for a demostration to anyone. I hope it is recorded in the code system to help in solving the situation.

The ASR box located under the hood is only a electric motor that is commanded to close the throttle. I doubt it can be made to open it. If any codes exist they could be ASR codes. Also, the cruise control located above the battery could be pulling on the throttle cable. Check operation of that unit.

 

[Schrade]

Did the dealer plug in to the ECM?

That should have told right away what happened. Engine controls are in the computer memory, although I don't know how long they stay there. But if it was taken to the dealer, they should have known right away, ESPECIALLY since she started it again in the intersection, and it pegged again.

I don't think this is guessing game Pin-The-Tail-On-The-Donkey...