Pizzano

Sorry , wasnt paying attention to the year, I had the same prob with my 88, set the IAC and TPS and solved the problem.

Tripleblack90

OK--here it goes. I change the IAC and the TPS first. I posted here and the recommendations that came back pointed to the Throttle Body which seemed logical as the shaft on the original one was sloppy. I ordered a new throttle body and installed it. Same thing. The car started up and idled fine. When I take off it acts as though the throttle sticks. It will idle around 3000 until I either kick it hard once or if I shut the car off while driving it and restart it the idle goes back down. I pulled it back in the garage and it was idling at 2000 rpm. I put the car in neutral, shut it off, restarted it and the idle went back to 1000 rpm. It has to be something electronic as the moment I shut the car off and restart it, the idle is fine until I give it gas

jsup

Again, on my car the injectors caused a surging idle. It would also surge when I was driving with my foot off the gas. It would surge from about 800 RPMs to 1200, back to 800. When I gave it gas it never settled down.

Did you check the injectors? Just for the hell of it. It's cheap, easy. Better than trouble guessing.

Since you're getting no codes, you should limit it to those things that do not throw a code.

Tripleblack90

I have not tried the injectors. It stays at 3000 until you shut the car off or kick it hard. You can see the throttle plate move back when you shut the car off.

Tripleblack90

????????? ????????

Tripleblack90

????

Sam Lam

Do the simple things first....like making sure the TB butterfly/cable is not sticking.

williammackean

I still maintain that it is your EGR system. One of the valves, controls or the EGR itself is causing the leak.

Pull the control tube as close to your intake as possible, plug that line and try it.

Injector won't cause it. Disconnecting your throttle cables would correct it, but it didn't. Wiggling your TB shaft would cause a variation, but it didn't.

PCV valve may be stuck open, too.

schrade

Every one who has advice for this problem has not the best diagnostic skills.



Erratic idle? That means it goes up and down with irregularity.

Next sentence, you say if you DO a particular thing, it changes.

Was it changing (erratic) already??? Or does it idle at 1200? THIS WE MUST KNOW FIRSTYou can do NO diags without knowing this


If it's erratic, START by looking for vacuum leaks.

If it is NOT erratic, and it 'hangs' at 1200 (or ANYTHING steadily), you have mechanical problems (carbon TB fouling, or pedal linkage binding).

OR, if it is NOT erratic, and it 'hangs' at 1200 (or ANYTHING steadily), and depressing the clutch changes the idle, you have an electrical problem.

Wizard out.


EDIT:
IAC, TPS, and TB. You must be loaded, slingin' all them parts blindly at a problem.

Feel free to wing some $$$ my way.

Tripleblack90

The definition for erratic is "inconsistent, not predictable or regular". It will idle fine when you start it, say 900 rpm. If you give it some gas, then the idle will "hang" anywhere from 1500-2500 rpm , it will not fluctuate, it will stay somewhere between the 1500-2500 mark, depending upon how much gas you gave it. The only way it will idle back down is to either blip the throttle hard or shut the car of and restart it and the idle will settle back to 900 rpm. With labor rates around $75-100/hour plus the fact that the throttle body shaft was bad, I have a total of $250 invested with $200 of that being the throttle body. So in essence, I have $50 invested in it and I know I couldn't have had the throttle body changed for $50. Long story short, I have saved money but still have a problem.

schrade

OKAY.

So whatever the idle speed is, high, low, redline, whatever it's turning at, IT STAYS THERE AND WILL NOT CHANGE BY ITSELF.

First try the pedal linkage. Warm up the motor (fully warm), disconnect the linkage at the TB, and then work the TB arm to try to 'hang open' the butterfly.

If it CAN hang, the pedal linkage does NOT get the rap.

If it does NOT hang, you cannot necessarily rule out the pedal linkage. Try lubing the linkage, and re-assemble.

Try that and post results...



Re-readin' your OP...
EVERY time you push the clutch down, it revs up?? And stays there?

schrade

Hmm...

Vehicle speed sensor, or vehicle speed sensor buffer...

???

Sam Lam

Before I would take the car to a Chevy dealership (they will be smiling as you come in), see if you can find someone in your area to use a scan tool on your car. See if you can find a Corvette Club in your area and contact them. They can lead to someone who can scan your car for you and you will may not have to leave your wallet with them Why hell, if you lived in the St. Louis area, I would do it for you just for a cold Bud Lite

Tripleblack90

When you push the clutch down it releases the load on the drivetrain that will in turn let the engine free up. The million dollar question is "why will it idle at say, 2200 rpm with my foot off the gas while coasting down the road. If I leave my foot off the gas while it is idling that high, shut the car off and restart it without touching the gas, it will now idle at 900 rpm."

johnnyevans

One other thing that you may want to try before bullets or the dealership is take the cruise control cable loose at the throttle body. I had a hang throttle problem and this resolved my problems, readjusted the cable, at the cruise module, and problem solved.
johnny

Tripleblack90

I unhooked the cruise cable and ran it for awhile without it. I had it at the GM dealership with the "corvette specialist" for some other problems. $2500 later I decided never to return. Currently heading to Menards for a gas can and a grille lighter :-)

Midnight 85

Which throttle body did you buy? A guy I know bought a new BBK and he was having a similar problem, the pivot on the tps was hanging up on the tb casting. He filed a bit off the casting and problem was solved. It's free and worth a look. I realize it was doing this with the old tb too but it's still worth a look.

schrade

Bingo. (I think)

Vehicle speed sensor, or vehicle speed sensor buffer.

Stick or auto, if you're coasting to a stop and put it into neutral, it does NOT go all the way down to idle speed, UNTIL you're at 0 mph. Under normal circumstances it will go only down to about 950 - 1150 rpm's, until you come to a complete stop.

I don't see ANYTHING else. If it is something else, you will find it by doing the diagnostic procedure for the VSS sensor.

RandyJ75

He bought the throttle body from me, and it worked perfectly on my car.

65Z01

Here's an idea:
-disconnect the throttle cables from the TB
-start her up
-manually run the throttle up/down as you would driving
-release and see if it sticks

If it sticks, cables are not the issue; if no stick see where the cables are hung.