camarosource

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!!!

Rice Killer87

WOW...thats freaking wierd man. Sorry I dont have any ideas for you but good luck on getting it fixed !

AutoRoc

My Holley carb never does that. It sounds wierd.

tom2

Have seen this with a bad throttle position sensor in the earlier cars like this. Don't know why it would cause this but it does.

Red89GTA

What does the computer show for TPS values?? Also, see if the car still does this when the vacuum line is disconnected and plugged. If condition persists then you know it is electrical not vacuum.

Lets us know.

Marc 85Z28

A failing sensor will not cause that engine to rev to 7000RPM

The only way you're going to see those kind of RPMs is with air, and alot of it. Either you have a monstrous vacuum leak (brake booster perhaps?) or the throttle is sticking open. I bet you could completely remove the IAC and it still wouldn't provide enough air to rev that high. Personally I would check the throttle and TV cables first for a binding condition. Then check that brake booster for an internal leak.

Edit: Is the engine actually spinning up that high, or are you just going by the tach?

RealDealZ28

What he said! I had an '88 Camaro a few years ago, and when the tach went out, it would still read, but was easily 2-3,000 RPM's off. If you have access to a scan tool (Autozone or Advanced Auto will probably have one you can use), it will monitor your RPM while the engine's running and the scanner is set to diagnostic mode.

From my experience, the factory tachs in these cars suck. I've got to agree with Marc 85Z28; if that engine is really seeing 7k RPMs, you're going to be picking up pieces VERY soon.

camarosource

Believe me, when I say the engine was revving, I MEAN IT ;-) So fast it was hard to hear the person beside you, and everyone a block away was looking and giving us VERY bad looks (especially "FLOORING IT" while stopped at the red light with tons of people and cars around in front, behind, and beside me....

camarosource

We found the culprit to the mysteriously HIGH revving engine and you won't believe how SMALL it is! Turns out that the mechanic who INSTALLED the rebuilt engine broke the pieces my Crankcase breather tube rubber 90degree elbow. It SPLIT twice down the middle of the end that fits into the TPI and decided to tape it up with BLACK ELECTRIC TAPE. As a result, there was NO grip on the male end on the TPI Vapor breathing inlet so there was just air and vapor bypassing. Well the elbow was the BEGINNING of the reason for the problem, the MAIN culprit was the IAC motor. The washer for the IAC was not installed, or probably broken for the looks of things and so oil and sludge started to cake inbetween the sealing and so the IAC could not fully close and would in fact open up pre-maturely.

I know it is the MECHANIC and not the engine builder or anyone else simply for the fact that I took pics of the engine in the car moments before leaving the car at the mechanics shop. I also have pics of the engine OUT of the car, pics of the newly rebuilt engine OUT of the car before it was installed by the mechanic, and pics of the engine IN the car.. And the black taped up elbow is ONLY shown on the newly rebuilt engine IN the car! The problem is you cannot buy this TINY, El-CHEAP'o part.. GM don't sell it.. and no one can offer it. I've even called around to wreckers and no one has any.. So a mechanic working on the car now is fabricating one but he claims won't last more than a month unless I find the real one.

It basically looks like a black rubber spark plug elbow..

Looks like this http://www.924.org/parts/PartsPics/82931intakeelbow.JPG except the inside is around 1/4" thru & thru. You can find this elbow directly below the passenger side of the TPI (looking at the engine from the front of the car). The inlet is directly below the TPI coolant inlet tube that resides directly above the breather tube

Osmosis

I'm wondering if you had recently replaced your tail lights?? I had a similar type of a problem after I installed the wrong bulb in the tail lights! I would hit the brakes and my idle would go up, turned out the tail bulbs = the problem>>..who would fiugre!

smokin25th

My car use to idle at 800-1000 when I lived in Wisconsin. Car sat here for 10 years in Las Vegas, I spent 7K on the car for mechenicals but the car idles at 1500-1700 rpm. The shop can't figure it out the prob. so I come and speak out for help... Don't get me wrong the car run HARD!! But the idle is just strange!

tom2

Nine times out of ten, this is a vacuum leak. Your idle air control is probably shut down but still getting air into the engine through the leak. Check all hoses etc. for leaks, or plug them off one by one and see if it helps. Then it could be the Idle Air Control IAC motor itself.