'93 vette. Going approximately 45-50mph, cruise control not engaged, the car suddenly accelerated wide open running the rpm's up to 7-8. The gas pedal was not stuck. It was not on the floor. Nothing was on it. Tapping the brakes did nothing. I stood on the brakes in an attempt to stop. The brakes were very "hard". The car somewhat slowed but would not stop. Any idea what has caused this? Upon stopping the car via throwing it into park to avoid a multiple car accident, turning the car off and on it continued to throttle wide open. Towed to nearest dealership in small town. The following day they can not reproduce problem. "Best guess" is the speed control adjuster GM 12557971 is going out. Expensive guess. Expensive part. And no longer available. Only one located used on eBay so far. Does this sound most likely problem? There was no warning, no indication of anything wrong. The only other thing I can point to is over the past year, most often while on the freeway with cruise control on, the car would "buck and jerk". I've had the injectors and everything else checked that could be causing this with no luck diagnosing. Could this be a sign this part indeed wasbeginning to fail? Thank you for any help.

 

The only way an engine can accelerate is to open the throttle to let more air in. Since your throttle was closed but it still wanted to accelerate it must have a massive vacuum leak someplace. The first thing that comes to mind is the vacuum hose coming off the brake booster, it is about the biggest vacuum source. Check that hose first.

 

A bad tps will do that.

 

But a massive vacuum leak would be obvious and just not go away, correct? The car is at the dealership and now will start and idle and run and purr like a kitten! It has been idled and driven for two days now with no repeat, so I would think that means something is "going out" on the car and I have been warned once by it. I need to find out what "it" is before I get into a disasterous situation such as Atlanat traffic the next time.

 

So the dealership didn't find anything wrong with it? You definately want to get that fixed whatever it is, that's very dangerous if your not expecting it!

 

There should be codes set likely, I believe there's an ASR light and lot's of diagnostics. I believe before I started throwing parts at it I would do some diagnostics that would be TPS related. The first part I'd throw at it would maybe be a TPS.

You could check cables to the ASR and check the procedure for the adjustment of the cables etc. I've read I believe ( I don't know) that there's a specific procedure for transmission throttle adjustment as well as accelerator cable that is related to the ASR. There's a short cable pedal to ASR and then a longer cable ASR to throttle body.

You likely don't have a Factory Service Manual but see if the small dealer if it's a Chevy store has a FSM for a '93MY. Might not. You can't fault the small dealer much for diagnostics, there's large dealers and Corvette specialty shops that might have problems with an ASR problem.

You might likely do better here in this thread with possible problems.

It needs checked for codes and an ASR light "first" I'd say. I don't know if the ASR light cycles in a "bulb check" with the key on or not but it's maybe one of the first things I might do is a key on bulb check!

Someone with an ASR maybe a '93 should respond soon I'd think. For the time being keep your money in your pocket!!

 

Pardon me for being a skeptic, but the description is really confusing. The 93 tach only goes to 6K unless it is a ZR1 and you can't put one of those into "Park". Doing that would be virtually impossible if the throttle was open anyway and if it did happen the transmission would be trashed????? Really?

 

I understand the skepticism BUT I believe if most would get into a "runaway stuck throttle" situation with maybe stopped traffic "dead ahead" they might relate the story similarly! No one has said the trans is fine, it's something else that maybe needs checked as well as maybe the "drivers seat cushion" for stains!

 

I am not looking at the car and/or the dial as it is at the dealership. I am repeating numbers stated to me by those working on it. As the driver, all I can say is the needle on the dial was up over halfway whatever that number is. I wasn't exactly looking at the time to read the actual numbers. I did know to be concerned if it red lined. I can not even tell you how fast it was going as I was not looking at that dial either. I was pretty much concentrating on a safe solution. If the techs are taking "liberties" in talking to me I don't consider that an issue. And the transmission is being looked at after the grind going through reverse while throwing it into park.
I am simply asking for some experienced advice as the dealership is not 100% sure of the problem, and I need it fixed. I have owned this vette for 15 years. It is my third vette having previously owned a '75 and a '85, but it if makes you feel any better I will admit to being a blonde female.

 

Thank you. I have asked the dealership to check the TPS and the IAC. I have also called and suggested the car is "coking" and parts need to be taken out and cleaned with a very good carb cleaner per another larger dealership. I,too, am leary of throwing money at parts, and perhaps used parts at that, without in fact knowing the exact culprit.

 

Surely the dealer has driven the car if they stated they can't find a problem. Given the obvious inaccuracy of the description how do we know what other facts given are accurate?
The hard brake pedal does sound like the throttle was open, that much seems true.

 

I do have the big, thick FSM for this car. Actually is there perhaps two of them? I had the car when I got married and my husband spent the money to have them here on hand. Seems like I may have seen him with more than one. It's not important, but I'm sure if I'm incorrect the other person that keeps writing will be quick to point that out. I appreciate everyone's valid help and input. I'm going to unsubscribe to the forum now as it appears some have a lot of time on their hands and are more interested in bashing others and making smart comments than helping fellow corvette owners. My husband seems to have some good dialog going on about the problem over on another forum. Thanks again for those that tried.

 

My apology, no disrespect intended. I was simply attempting to point out what seemed confusing concerning your description of events. I do understand how stressful such an occurance would be.
Best of luck sorting out your problem.

 

Thanks, but I'm not on here to be harrassed, harangued or belittled. I was simply hoping to find some nice people that could look at the big picture and give useful suggestions or relate if they had similar experience. It's really not that confusing. Straigh forward. Throttle open. Car sped uncontrolled. Pedal not stuck. Cruise control not on. Tapping brakes did nothing. Putting in neutral did nothing. Standing on brakes seemed "hard" to me, nonreactive. RPMs rapidly climbing.
Stopped car by throwing into park, risking my transmission instead of other's lives and injuries.

 

So about how fast were you going when you put it in park if this started at around 45mph? What did the car do when you did that?
The dealer has the car and they cannot find the problem, if you want us to diagnose it all we have to go on is your description, if that is not accurate our chances of success are pretty slim.

 

4 lane road. Speed limit 45. As a best guess that puts me 45-50mph when it started. I would have been below that when took the drastic action of potentially scarificing my transmission, but I did not look at the speedometer ANY time during the entire thing. Speed was not my primary concern at the moment. The car would have been slower as I was standing on the brakes. The transmission tech at the dealership said he would look at it this afternoon. Speed, trans and stopping has nothing to do with diagnosing the problem as we are trying to discover why it STARTED in the first place. In hind sight perhaps I should have turned the key off but was worried about the steering locking on me and feeling more panicked and helpless due to total lack of control. Husband suggests I could have turned it the one notch to turn off the engine but not lock the steering. If I could do that while in the middle of trying not to hurt anyone perhaps I'll remember that next time. It still has nothing to do with diagnosing why the vette started this in the first place, which is all we are trying to do. If I fix anything and everything else on the car I do not want an expensive repair that is only a "guess".

 

I have had one of my corvettes do that with an aftermarket throttle body with a stiffer spring. The cruse control would go into WOT if it was on, I simply turned it off and the throttle returned to normal.

 

Yea, well hind sight is 20/20, but when your car is floored like that and you are in panic mode it's hard to react! At least yoru safe!

My 70 Camaro did that 32 years ago, but I was drag racing on the street and luckily I somehow put it in neutral instead of park and turned off the ignition and all disaster was diverted!

 

Somehow, every other poster missed this.

I bet you had a catastrophic vacuum leak caused by a failure in the brake booster.

A large vacuum leak will cause the engine to race, granted you have little available vacuum to the booster for braking with the engine at high RPM. However, I would check this out.

The hole/cracks may not be evident but must be there the flexing running of the car may cause them to open up. You could try to run the car in park and idle and mess with vacuum lines and things as see if the RPM's change.

On a gasoline engine RPM is set by how much air is being allowed into the engine. IF the throttle blades are closed, it has to be getting in ease where.

FYI, I would not worry about shutting the car off either. Just steer and try to stop. Simply bump the shifter into neutral it will go without hitting the button the side. Assuming its a automatic. The rev limiter will protect the engine. If a stick, simply push the clutch in.

 

I beg your pardon, my post was the first response and while I didn't get technical as to the exact source of a possible vacuum leak I kept it simple just to get the OP steered in the direction I felt the problem was in.