Tripleblack90

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Sam Lam

Did you have someone scan the ECM to see if the root cause of the problem could be identified? I re-read the posts and did not see any comments on the scan idea.

Tripleblack90

Nothing came up on the scan.

Sam Lam

Did you find/solve the root cause of your '90 model idle problem?

SAM

j-wireman

TripleBlack90, I had idling problems, too. Replaced the IAC, Man. Air Temp., Coolant Temp. Sensor, cleaned and re-cleaned the T.B., cleared all codes, with no results. Finally gave in and took it to a dealer (they have a Corvette-only technician). He found a Hypertech chip on the ECM, and that the computer was screwed up (idle speed erratic, RPM's didn't match tach, etc.). He put a new ECM in and she runs like a top.

Just my 2 cents.


Mike
'90 'vert

Sam Lam

TripleBlack90: I asked if you had considered having someone scan the engine fuel management system. Your comment was that nothing showed up on the scan. A scan of the ECM is similiar to having an X-ray taken of your body. A picture is taken and someone with a high degree of experience reads the X-ray and determines the root cause of your problem.

I assume you had someone attach an electronic device to your car ALDL connector and then exmaine the data from the ECM. Is it possible that someone checked for engine codes and you thought this was an engine scan?

Just trying to help you

Tripleblack90

Changed back to an old throttle body. Problem gone. Apparently the unit from Extreme-FI is junk. Wish they would have returned a phone call.

jeffp1167

I have a firebird with the TBI V-8 motor in it. It does this same damn thing cooler weather only makes the problem worse. On the hotter days it is for the most part fine but when cooler I am always having to wrap the accelerator like you do unless I let the car warm up to operating temps before moving it. But then as motor cools while driving back comes the sticking problem. Yes mine is a 5 speed to.

My best friend is having this problem with his 90 six speed vette now to, I am almost inclined to believe it to be the AIT sensor mine has this mounted in the air cleaner, But wouldn't it throw a code? I know my ECM is fine as replacing it made no change, grounds are good, etc etc.

But like I said my condition is more prominent on rainy and or cooler days verses 80 degree days. My firebird has functional cowl induction which is open all the time, yet it also has the heat riser off the exhaust manifold going to the air cleaner. I've run into other TBI owners who have had the same issues that have never been fixed and theirs reacts to temp changes much like mine.

I've never read about anyone replacing these AIT sensors or heard of one giving problems but is it possible they could not light the check engine light up? Maybe if they are responding slowly the ecm wont detect a problem. Could the rushing air difference from mashing on the accelerator quikly make the AIT sensor react and make the idle change?

I know for a fact my egr is working correctly, TPS is set correctly, injectors are spraying fine, throttle cable is not the problem (car will do this with cable off) I can see the throttle blades moving freely and there is no resistance when moving them by hand.

could carbon buildup be the issue? Being when its hot it not causing a problem but as it cools thats when things start sticking?

Don't feel alone TBI engines do this Too LOL

Tripleblack90

Mine was a circumstance where it would only stick when the motor was running otherwise it operated freely.

Tripleblack90

Well, I thought the problem was solved but it is back. I put a new motor in it, it was due, took it for a 300 mile trip, and then the idle starts acting up again. Idles fine, rev the motor and then it will idle high until you kick it once...... I hate this car.

jeffp1167

do this move the throttle linkage from under the hood and you will see it stick (space between linkage and idle stop screw) My 90 auto does this! It's cause by the the throttleblades wearing into the bores and the fact the stock return spring over time has weakened. Try a extra carburator return spring and the problem will go away. It's that quik snap of the accelerator that forces the throttle blades shut.

Tripleblack90

When the car is running, the vacuum will hold it open. If the car is not running, it returns fine. Engine vacuum, not a worn throttle blade, will hold it open. It is a new throttle body. I put springs on it that will overcome the problem but then you need a lead shoe to depress the accelerator pedal. Thanks for the reply.

jeffp1167

engine vacuum overcomes the stock return spring? That seems impossible is there any return pressure from the spring? my best friend said he had this sort of problem with a new throttlebody to his idle problem got worse. Try this buy a cylinder hone for a small bore and try and remove any areas that the throttle blades are hanging up on the original throttlebody. then loosen the blades set screws to center the blades and retighten them. maybe that will stop the blades from hanging up

Tripleblack90

I will try this. When the car is not running, it seems to operate very freely. When it is started, the vacuum will not let it close when you idle it down slowly. It seems so simple yet I have had several different people look at it to no avail. Thanks for the input.

Tripleblack90

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