Hi everyone! Hope I can get some ideas here.

I am not a mechanic but do have some friends with automobile knowledge.

I will try to give as much info as possible and I would like to thank everyone beforehand for your help.

My car is a 1990 Corvette, 68,000 miles, L98 350, Automatic transmission.
Driven and garaged in Indiana (warm somewhat humid summers).
Since I have owned the car has always used Shell V-Power NiTRO+ Premium Gasoline.

My car has run fine in the past and all of a sudden when stopping, the car revved up to about 2000 rpm (warm engine).
I put the car in neutral and tried pushing the gas pedal hard to see if something was stuck, but this didn’t help.
I then drove to the next stop sign and it continued to idle fast.
Once through that stop sign, I drove about 20 miles with no issues before I had to stop and everything was running and idling fine.
This issue didn’t happen again for a few months (same scenario as above).

After the second occurrence, I decided to give the car a tune-up (plugs, wires, distributor cap, rotor, coil).
After this, the car would run fine, but would still randomly do the idle issue.
Over time it did seem to occur more often and a few times it even happened right after starting.

Over time the car got worse starting to rev up and then die driving down the road.
At first, it would start easily after an episode but then was becoming harder to start until one day it wouldn’t start after dying (would crank but not start).
I’m thinking fuel pump and/or fuel filter at this point since I never smelled raw gas.

I had the car towed to an auto repair place that claimed to have worked on many corvettes before.
I did mention the fuel pump and the first call from them said they checked that and it was bad, so they replaced it and the fuel filter.
Still wouldn’t start so they thought it was the ignition control module and replaced it, still no start.
The next time I heard from them, they claimed it was the ECM and I okayed replacing it.
I got a call that it was ready to pick up and the ECM had fixed the issue.
I picked up the car and was driving it home (about 25 miles) and after 20 miles it did the same thing it was doing before but would start after the occurrence.

I tried driving it a little (very short trips, less than 5 miles) and it would act up every time.
After being stored for the winter, it wouldn’t start because of a dead old battery so I replaced it and it will start.

I tried letting it run in park and in drive for 30+ minutes 2 different times and could not get it to act up.
Drove it to a parking lot about half a mile from my house and drove around for about 15 minutes and it revved up and then dyed.
Had to wait 10 minutes or so before it would start. Idle was very erratic but I was able to limp it home.

I haven’t driven it since then, don’t trust it.
This was kind of long, but I wanted to give as much info as might be needed to receive some ideas.
No error codes available.

 

Hello.
I have owned 1991 C4 in Japan for 30 years
I've had most of the trouble.
(I've been to this Corvette forum for the first time)

Your symptoms can be multiple troubles.
Also, unfortunately, parts that seem to be new may be suspicious.
It is recommended to change in the order of TPS> IAC> Pickup Coil.

 

Hello There MrKarma and Yoshio!

Welcome to the Corvette Forum! This is the place if you have questions about a Corvette.

While driving your Corvette on the roads it is likely in "Closed Loop". This means it is constantly reading the Oxygen sensor, the coolant temperature sensor and Mass Air flow sensor. It is likely one of these three that will lead you to the problem. How old is the O2 sensor? If it is over two years old it is time to replace it. The newer sensor is more accurate and faster reading than one that has seen years and years of service.

Your Coolant Temperature Sensor plays a HUGE role in the fuel system by telling the computer how hot the engine is. If the CTS is bad you would have a harder time starting it either when it is cold or when it was hot. If the sensor thinks the engine is cooler than it really is then the ECM adds fuel to help it start and run in colder weather.

Your M*** Air Flow Sensor is there measuring the air volume being ingested by the engine during combustion. It is a very important sensor and easily made less accurate by crud building up on the sensor wires (1/10 diameter of a hair). They make spray cans of a special solvent to clean the MAF sensor. Sometimes it works and sometimes it doesn't. Be sure that there are NO air leaks downstream of the MAF and the throttle body, if there are seal them. You can have NO air leak in or it will mess up the drive-ability. The MAF system uses two relays, one for controlling the power and one for the Burn-Off Function. If either relay fails so does the MAF sensor so always replace both relays when you replace the MAF sensor.

On my 1988 C4 there is a Cold Start Injector that is installed on the plenum on the rear drivers side. I have heard of the CSI's failing and adding gas to your idle making it idle slightly faster than normal. The CSI is there to act like a Choke on a carburetor when it is cold. When it comes on the idle goes up for a bit. I think you can unplug the sensor from the CSI and disable it for a test. I wonder if the CSI is giving it so much fuel when Hot that it stalls the engine. The thermo switch may have failed and allowed the CSI to work when warm. Try to disable it and see what happens to your Corvette.

I would clearly check the Fuel Pressure to eliminate that as a cause. If you don't have a Fuel Pressure Gauge they have them at most auto parts places, some will lend them to you. I bought one as I use it a lot.

You could check to see if the CSI is activating by checking it's power connections. The CSI simply squirts fuel into the plenum to assist in cold starts. It was discontinued a couple years after my C4 Corvette was made.

You might double check your Fuel Pump Relay, they are cheap and easily replaceable. They can heat up and fail. Mine had a bad crimp connection which made it miss when I hit a bump. If nothing has helped so far I would start at the battery and measure the voltage. Then go to the fuse panel and verify that you have the same or very close numbers. Verify that the fuel pump is in fact getting close to full battery voltage. An older FP relay might not be able to hold the contacts closed if it doesn't have sufficient voltage. I keep a spare FPR relay in my glove box as it is used in several places.

If you don't have them this is a short list of important tools for working on the L98 Corvette:
1. Factory Service Manuals for your particular year Corvette available from Helm Publishers. The hard copies are not cheap, about $80 for the set. You can get the FSM on a DVD on Fleabay for a fraction of the price. (~$25)
2. Scanner or Cable and Software to read your computer. These are extremely handy when you are chasing a weird problem.
3. Fuel Pressure Gauge
4. Digital Volt Ohm meter

I hope that this will help you a bit. The more I think about it your problem might have something to do with the CSI circuit.
We are here to help so let me know what you are finding and we will try to help solve it for you! Also remember to keep your battery and ground connections CLEAN. I have seen serious voltage drops in Corvettes and it is frequently caused by corrosion. I keep a small bottle of DeOxIt with me in my tool bag. DeOxIt will remove decades of corrosion from light sockets and any other connectors. I tried it on the rear of my C3 and the brake light was noticeably brighter after the socket was cleaned on one side.