I have a completely stock 1988 coupe with about 75,000 miles. I had the car die on me a few weeks back, after making a couple errands stops the third time I went to fire up the car it wouldn’t stay running; it would cough, shake and die. I had to have it towed home. There were no codes from the computer. I thought it was an IAC, it likes to consume those; but no dice. A few members of this forum said I should check the MAF, which I did the next morning. I unplugged it and the car started right up. I plugged it back in and cleared the code that generated from running with it unplugged and took it for a short drive; it seemed fine. The next day I drove to work; stopped at a store along the way and when I came out it didn’t want to stay running; not as bad as the last time; I was able to make it to work; but it was rough. It seems to clear up some after the car sits for a significant amount of time, say 8 to 10 hours, but not perfect. I have changed the IAC, cleaned the MAF and last night replaced the MAF, same problem. There are no codes. I love this car, but issues like this keep coming up; it has eaten at least 4 IAC's over the last 4 years; which is troubling to me as well. Any ideas of where to go from here?

 

You Might be experiencing a fuel injector failure. In 1 or more cylinders.

Or are you sure that you have a good-proerly working MAF Sensor? You failed to mention in the MAF sensor you replaced the original with was a GM New part or a used Junkyard unit. Cleaning out a MAF sensor with the wrong type cleaner can damage a properly working MAF unit. CRC makes a MAF sensor cleaner. The only cleaner I would reccommend.

There are a lot of variables to work with here. You also need to check over all ignition componets. And a fuel pressure check with an accurate guage such as a Snap On unit would rule out any fuel pressure issues. You can also monitor a fuel pressure drop from a leaky injector as the car sits not running over 15 minutes.

You may need to find help from a very compentent mechanic in your area with experience and the correct troubleshooting tools for driveability problems with your Corvette.

Write me back if you wish to try and repair your Corvette yourself. I will try and help You. It would be easier though if I was there first hand to troubleshoot myself.

Brian

 

If I'm not totally wrong it should run even with the IAC all the way closed. There is a minimum air adjustment under a plug on the throtle shaft. I had to adjust mine once. Did you clean behind the throtle plates? Also look at engine grounds they can cause a lot of problems.
The MAF can be going bad when it gets hot just unplug it and see if you can drive it. I've seen some of the V6 cars just pull up to a stop sign and die. Unplug the MAF and you couldn't tell a thing besides the check engine light.

JS

 

When you did your MAF, did you do the power and burn-off relays?? GM had TSB's on these as they were troublesome for providing poor or intermittent voltage levels. They're located along the firewall behind and just below the cruise control module.

 

Thanks for all of your suggestions: I replaced the MAF with a reman unit from Auto Zone; I had used the maf cleaner you suggested first a week or so ago, no help and no change when i put the new one in. I purchased new relays but they didn't fit; so i tried the new MAF with the old relays; which i guess could be an issue. As far as fuel injectors; I had them all replaced at a Chevy dealer a few years back so they have less than 10,000 miles on them, I know that doesn't mean they are not bad; but it seems unlikely. I have cleaned the throttle plates, but I have not checked the grounds; I'll do that. I will also try getting the relays from GM and see if that solves my problem. If not; I do have a pretty good mechanic I can go to; i just didn't want to spend the money.

Thanks for all the suggestions.

Mike

 

There's nothing worse in troubleshooting than dealing with an intermittent problem. For this particular issue, a scanner would be really useful. If you could find a copy of the old Diacom software and a cable it would help tremendously. You could hook it up and monitor values as it fizzles out and get a better idea of the area to chase.

Have you monitored fuel pressure while all this is taking place?

The good news is that it sounds as if, given enough time, you can duplicate the problem. Most intermittent problems don't follow a time schedule, making them even tougher to deal with.

Also, just use a DVM across the battery and monitor battery voltage from the time you start it until it dies. A screwy alternator or problematic connection such as a bad ground or screwy fusible link could be worth checking if battery voltage trails off.

Good luck,
Doc

 

Thanks for your suggestions. I dont know how to monitor fuel pressure, so the answer to that question is no. I can check the voltage and I will to see if there is a clue there.

 

You can get a fuel pressure gauge at most auto supplies and they're not very expensive. It connects to a Shrader Valve connection on the right side fuel rail near the rear. It would be a key thing to check.

Good luck,
Doc

 

Thanks for the advice; I'll pick one up and see where it takes me.

 

This sounds eerily familiar. My intermittent problem on an 88 turned out to be a bad wire to the fuel pump, right at the entry to the fuel tank (in the molded part). Another member chimed in with this exact issue on you got it, another 88. YMMV!

You can roughly check for fuel pressure with a screwdriver or key. The yes-no will eliminate a lot of other guesswork when working marooned or without the manual or real tools.

On the passenger side top of the engine look for something like a larger version of a tire valve stem cover (but aluminum, and pointing "up") on the fuel rail - this is the valve where you will/would attach a fuel pressure gauge. When you have symptoms twitch the valve stem and see if your pressure is low (ie like a water bubbler, as opposed to a Pfft), I'll bet it is. The small amount of fuel you'll disperse is hazardous of course but will evaporate very quickly.

If fuel pressure is low, it can be related to spark problems too as the fuel relies on spark for the signal to run. When symptomatic, spraying a few seonds of starting fluid on your air filter should cause the engine to run smoothly for 5-odd seconds. This confirms spark is fine and your problem is just fuel.

For more of my recent trial see my recent thread "who stole my fuel pressure".

Good luck, I was blessed with a lot of great help here.
- Jeff S.

 

I just wanted to take a moment to thank all of you for your response to my issue; turns out it was a fuel pump and I am back on the road.

Thank you all again!!!

Mike.