1987(late)
Problem:

Every spring for the last 3 years, my corvette dies at idle.

At the start of spring (45-50 degrees, humid St. Louis climate) the motor stops running at idle. If I give it gas (and brake) at the stoplight/sign it will stay on.

Yesterday we hit about 60 degrees. Same problem, with the addition of the motor dieing while giving it gas. When this happens, it takes a couple of tries before the motor will start back up.

In the heat of summer, the car will die more often, and the time it takes to start back up is increased significantly.

What I've done so far:

I have replaced the Idle air control, electronic control module (right name? black electronic peice, located under the dist cap), dist cap, coil, fuel pump and relay, and spark plugs. Alternator and battery test fine.

I have never let anyone work on the car before, and I'd like to see if I can figure this out with your help! (I went to DOBBS for tires and the kid drove her up onto the parking block- I just can't handle the thought of someone taking her out on a "diagnostic drive")

Thank you in advance!

 

Have you verified if the ECM is controlling the IAC ?
http://members.shaw.ca/agent86/IAC%20Diagnosis.pdf

Have you done any fuel pressure tests ?
http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf

Have you tried to set the minimum idle and throttle postion sensor ?
http://www.lbfun.com/warehouse/tech_...ch%20Paper.pdf

Are there any stored codes ?
http://members.shaw.ca/corvette86/No...it%20Check.pdf

 

Thank you so much for the steps- going outside now!

 

IAC- done when I replaced it.

Just wondering, If the TPS and IAC were not set properly, I would still have the problems during winter months too, right?

Can't check codes- attached code reader and it keeps saying the vehicle is not connected. I do remember that there was a MIL for the EGR valve a couple years ago. No emissions here, so I ignored the light. The light has always been on, and I used to periodically check for anything new. The light is on now, but it wont connect.

 

All you need is a paper clip or a piece of wire, to read the codes. Jumper "A" and "B" on the ALDL connector, turn on ignition, and count the flashes of the "SES" light.
http://members.shaw.ca/corvette86/No...it%20Check.pdf

You replaced the IAC, but did you verify that the ECM is controlling it ?

 

Will verify ECM control of the IAC in a few minutes.

Um, I just jumped A and B, the service engine light did not flash or come on, but the cooling fan did??? When I removed the jumper, the fan shut back off...

 

Probably need to check if the bulb is still there or burnt out.

Does the check eng lite illuminate when the ignition is first turned on? It should.....

 

Thank you, it did not turn on when the key is turned to on. I removed the instument panel and I guess there is a bad connection. Light is working now!

If I did this right, I got codes 22 and 36... looking up now

 

22 tps sensor signal voltage low
36 ignition system circuit error

I guess the 22 means replace the TPS, but where should I start looking for 36?

 

The TPS can be adjusted if it is a good unit.

Agent86 can probably popup a link to the FSM trbl shooting guide for the "36" code

 

http://members.shaw.ca/corvette86/Code%2022.pdf

http://members.shaw.ca/corvette86/Code%2036.pdf

 

Update:

Had it towed to a shop for diagnostics. They couldn't get their tech scanner to read the computer. They said it was the computer causing the problems and it'd be $500 to replace. I said thank you and paid the $100 diagnostic bill and took it home.

Replaced the computer- same problem.

Replaced the Electronic Spark Control Module (mounted by the blower motor)- same problem.

The TPS reads .01 volts at closed throttle. I tried to loosen the adjusting screws per the diagram posted by agent (thank you), but the screws did not break loose. In fact, the screw heads broke off before making any sort of turn.

Any good ways to get the studs out without causing more damage?

Tomorrow, I will try and find similar screws (threads and head size at least), and begin adjusting the TPS. I will also remove the IAC, make sure the computer is moving the tip of the IAC, and test the MAF relays and wires



Oh, also, after replacing the computer, it has not thrown any more codes. Actually there are no codes at all, and I did let it run and die a few times to try and make it come on again...

Also, once the car dies by itself, when I try and start it again without touching the gas, the motor will turn on and run, but only for one second- dies just as fast as it started. If I give it gas and rev it up just a bit, it will run for a few minutes before dieing again (I think this is because of our weather today- slightly chilly, as when it is hot outside it will not turn back on for a while)

Thanks everyone

 

Your going to have to drill them out. They are aluminum ,so it takes little effort.
Find some stainless allen head machine screws and tap to match.
I could not find the bastard metric screw, 4.5mm is not a common size, so I tapped them to 5mm.

 

Are the trottle bodies replaceable with those off of other TPI's? Maybe I can save some time by finding one at a junkyard?

 

Holes drilled Thanks!

I turned the key to ON, with the IAC pulled from the TB. No movement.
I'm not sure this is causing the original problem because when it is warm it will die while the butterflies are open (and not restart while open too).

Also, I realized earlier that the motor stopping is usually after a few minutes of cooling fan operation. (This would explain it not dieing as much in winter because it is on rarely)
..........this is killing me!

Before I broke the screws, I was about the adjust the TPS. When I move the lever of the TPS to a reading of .54 volts, the engine goes up to about 1200 to 1500 RPM. I did this for a minute or longer (engine fully warmed up + cooling fans running) The RPM never came down unless I let go of the TPS lever and a reading of .01 - .00 volts

Thanks again everyone for the help- you guys are helping/teaching me a lot!

 

Diagnose the IAC, following this link.
http://members.shaw.ca/agent86/IAC%20Diagnosis.pdf