camarosource

iTrader: (1)

1992 Camaro Z28. 5.7L V8 350TPI with Headers, and Mild Cam...

Serious problem with car.. Idle mysteriously at random revs within 5 secs from norm to OVER 7000RPM at a dead stop

Couple days ago I got a new chip custom burned for my car. That very same day just as I came off the freeway I came to a stoplight with 1 car in front of me. As I was JUST about at a dead stop with my foot on the brake, the car acted like my brakes weren't holding the car back as it was idling to a complete stop. Turned out the engine was suddenly starting to rev from 2000RPM and the wheels were actually starting to spin. I immediately put it into PARK and the emergency brake on. The car is now REVING in only 5 seconds to get OVER 7000RPM.. The engine is shaking, my temp guage goes OFF the scale, and the moment I see SMOKE fly from under the hood I IMMEDIATELY shut off the engine. Blocking the intersection..

10 seconds later I start the car and the tach FLIES back around to normal, and the temp needle moves from 125+ to norm which is around 105 (NOT possible for an engine to cool off in 10 seconds like that).. But it ran perfectly fine. The guy who programmed my new chip worked on the chip at my workplace and thought everything was fine. UNTIL today!

With the GF we are approaching a stop with cars in front and suddenly it does it. I gets to 3500RPM and I immediately shut off the engine. I am now blocking the lane. I get on the phone with the guy and he says he will come to my house and work on it. 1 min later a car starts honking at me because he is trying to get out of a parking spot and I am completely blocking him. I turn the car on and it's perfectly normal.

He changes my idle, and we suspects a vacuum leak of some sort because it seemed to only do it when I braked. To experiment, he disconnected the Idle Air Control at the front side of the engine by the TPIS. Turn on the car at the idle starts at 3000/3500RPM which he says is normal. Now he tells me to start pressing the brake. After about 5 presses, and engine starts to increase in speed and actually starts to rev higher and higher.. He is BAFFLED.. I've talked to other mechanics on the phone and they are baffled.

We suspect it was the chip holding the Idle Control motor open so we put back the orginal stock GM chip. Tried it and AGAIN when you disconnect that Idle Air Control and press the brake a couple times the engine starts to increase speed.. It stays at the same RPM when you stop pressing the brake. Press it again and it starts increasing...

HELP!!! What is causing this???

Someone PLEASE go your car. Disconnect the Idle Air Control, tell me what your RPM is at on idle (should be high), and then what happens when you start pressing the brake pedal a bunch of times if your engine speed increases??

THANKS!!!

ljnowell

I guess in theory it could be possible that when you hit the brakes you are pulling an excessive amount of air in through the vacuum line to the brake booster. You stipulate that this only occurs while on the brake, right? perhaps you should pull the vacuum line to the booster and pinch it off. Then try applying the brakes and see what happens.

TheRealBlkBird

Wow, that's bizzare. I was gunna say put a stock chip back in but you already did, I dont know what to tell you.

Oh, I would've helped with your request but my battery's dead(one of many problems with my own car right now).

camarosource

iTrader: (1)

See this seems to occur when I WANT IT TO (Otherwise it's at random while driving and coming to a stop with the brake applied) ONLY if the Air Idle Control is disconnected at it's at 3000RPM when start up. THEN press the brake pedal a few times...

So... For sake of argument... Let's say we remove the vacuum line to the break booster. Put in a bolt on the end to stop it from coming thru as one mechanic has told us to do..

with the AIC CONNECTED, it doesn't normally rev higher; only when OFF.. So with the brake booster vacuum line off and with a bolt on the end, SHOULD it rev or should it NOT rev higher upon pressing brake.

It would seem that I would want to disconnect the AIC, AND that vacuum tube, THEN press the brake and see if it's doing it .. and seeing if braking still makes the engine rev higher ? But the mechanic told us to NOT remove the AIC when trying this.. I'm confused?

With the AIC connected, and vacuum tube disconnected with bolt in, pressing the brake.

Reving occurs concludes what?
Reving does NOT occur concludes what?

Thanks!

ljnowell

With everything else hooked up, and the bolt in the line plugging it, if it does rev up when you pump the breaks, that eliminates he possibility of it being the booster. If it doesnt rev up, and you cant get it too anymore, with it plugged, then you need to look to your brake booster as the culprit.

camarosource

iTrader: (1)

Well I THOUGHT this was all fixed when it turned out my Crankcase air tube to the TPI was cracked and leaking. Replaced it and all was fine UNTIL 2 DAYS AGO... It did it again!!

I was at a light. Then suddenly it started to increase the REV all byself! The floor mat was not touching at all. I was not pumping my brakes at all.. Immediately put it into PARK and it continued to climb till it hit 7000rpm which only took about 3 seconds till I turned off the car. Turn it on and the guage FLEW (SPRUNG) back to 0RPM and then immediately started to REV when the car was turned on.. Leave the car OFF for like 10 mins and it will fix itself..

I've taken it to 4 places, least 8 mechanics have looked into it, including the engine builder and no one can explain it. The stock chip was put back, it still did it, completely disabled the cruise, still did it.. Checked for vacuum leaks, none were found.. When I pump the brakes at the stand still the tach moves a SMALL amount which indicates a SMALL leak in the brake booster but nothing should cause THAT high REVVING. Even with it in park and foot OFF the brake it would continue to rev to max. IAC seemed fine when it was checked with a voltage meter. Butterflies are not binding, and cables are not found to be problematic..

NO ONE can figure out what is wrong.. and the problem is it will do it like once and not do it for another few MONTHS so how can you diagnose something when it won't do it for a mechanic.

Only thing I have yet to discover is whether or not the gas pedal is moving TO the floor. that would likely help diagnose something if it was..

ezysk

It almost sounds like a faulty Throttle Position Sensor (TPS)
I do not know what the default mode for it is, if you disconnect it.

Assuming your car is not modified to the point where you don't have a TPS.

If it were me, I would try this.
If you can get this to happen while you have someone with you.
Then as soon as it happens, put it in park, pop the hood and disconnect the TPS.

If the engine speed drops to idle, you may have found the issue.
If it does not, then you have someone with you to shut off the engine.

camarosource

iTrader: (1)

While that may be a solution, the problem is I would be redlining the engine BEYOND the tach the entire time and this is a newly rebuilt (1 year old) engine.