Good Morning Everyone,

We Have been mining the forum for a few months now trying to fix this ongoing problem in our 1989 Standard Transmission Vette, and are finally just at a loss, or at the limits of our shade tree knowledge.

We Purchased the car in August 2016 with 75k original miles on it, from the second owner. Had been garage kept and drove like a dream. Only issue we knew of was the heat didn't work, but being in Arkansas we honestly were not that stressed about that. Drove the car 2-3x a week without issues. Master cylinder was replaced in October, no problems. The fuel pump went out at thanksgiving and was replaced without incident. Battery was replaced in January 2017.

Car was dinged on front drivers side fender at work parking lot in March 2017 and because of parts availability we didn't get it back until May. Ever since then it has been having a terrible rough idle issue, growing to the point of it wont stay running at a stop without constant gas being given on the pedal.

This is what we have done in approximate order:

replaced 02 sensor
removed gunked up precats, Main cat is clean
Checked fuel injected ohms, those were in perfect range.
Replaced spark plugs (they didn't have cables in stock at the time)
drained and manually cleaned fuel tank, refilled with premium ethanol free fuel
Replaced fuel line and fuel filter
Reset timing, both using TDC and a timing light, and going through the proper unplugged 20 minute cycle with the computer. The distributor looks good and to be making good connection, but I am not opposed to the suggestion it might need replacement.

All fluids are clean and topped off.

Ran troubleshooting by unplugging mass airflow sensor and the MAT.

What the car does now is virtually the same thing it did before.

Fires up beautifully. Runs great up it reaches about 200 on oil temp. Then it starts to chug down to 500rpm on the gauge and the lights start flickering. If we dont "whomp" on the gas, it will die. If we give it gas, it will run again for about another three minutes. If we get it out on the road and reach highway speed, the SEL will come on, and it suddenly runs like a champ, but by the time we can pull over and try to run the code, the SEL is gone and its chugging again.

During all this the previously working cruise control has also gone out.

The only code we've ever gotten was for the 02 sensor, "rich exhaust". We replaced the obviously bad sensor with a new one and the code went away. Even with the precats gone it hasn't thrown that code.

We are trying to find someone who will work on it but are running into the wall of "we don't like to work on cars the owners have worked on". Which is a whole nother level of aggravation to me but...

Does anyone have any suggestions, ideas, or something obvious we are just missing?

 

If the ses light came on there should be a code, unless ecm is resetting. If you have a service manual, I would check ground circuits from ecm to ground. If you make a test light out of a reverse light bulb and socket attaching one side to positive and the other to ground terminal of ecm connector. If the light comes on the ground circuit is intact, dim - high resistance , out - open circuit. Service manual also has ground locations, you could see if wiring matches the illustrations. You need a scanner to monitor data to see what's happening.

 

Lets start with getting fuel pressure. For now, I would turn the key on and see if it gets to about 40psi and how long it holds after you turn the key off. When you turn the key on, it should cycle the pump for a couple seconds.

If that checks out, lets check spark. Go in the darkest place you can find and start the car. Spray a FINE MIST AROUND the wires and see if the wires are leaking.

After that, we can work on the rest of the idle with a scanner.

 

Check your vacuum hose's.. that was my issue but mine is a 84 crossfire.. just saying.. good luck

 

Did you try resetting or replacing the TPS sensor? Or cleaning or replacing the IAC check valve. I would replace both because they aren't expensive.

 

Thanks...but it wasn't my issue I just suggested check the vacuum hoses

 

Won't work on a car the owner worked on isn't that precious LOL. Translation I don't have the slightest idea how to fix this. Fuel pressure seems very unlikely at idle unless voltage is getting painfully low and still doubt it as a couple lbs. and hour is about all it needs at idle. I would look around at where they worked on it at the body shop for bad grounds wires unplugged etc. Going to the body shop and asking them would be a good idea as well. Don't look to blame anyone just end the R&D job finding it.

 

I can believe that. It is a nice way of refusing the job since they usually don't have enough mechanics that know or want to work on old stuff.