I have a 1989 Iroc Z with 305 TPI 5 speed. I've owned this car since 1991. Anyway, today I got it out of the garage, went for a 50 mile cruise and when I got back, I parked it. It ran perfectly the whole time. About 2 hours later I went for another ride and after about 3 miles as I was cruising down the road about 50 MPH, the car started loosing power, was bucking and surging. It would then intermittently run fine and then start bucking and surging again. While it was acting up, I noticed the check engine light would blink on and off intermittently. So when I got it back home, I checked for codes and there are none stored. I drove it again and it was fine. I let it idle in the driveway for awhile and and it started surging and carrying on until it finally stalled. Checked for codes again and none were stored. After about 2 more hours, I started it up. It fired up immediately,and ran perfect, so I put it back in the garage for the night. The car now has 213,000 miles on it. I changed the fuel pump and fuel filter at around 168,000 miles. The computer was changed around 150,000 miles. All eight fuel injectors were changed around 175,000 miles. With no codes stored any ideas where to start? Has any one else had similar issues, and it so, what fixed it?
Thanks.

 

My guess from what you've told us is it's starving for fuel, either from a clogged filter or a pump that is failing.

 

My guess is it sounds like electrical. Something is getting warm and after it gets warm enough the electrical component is going partial open, then when it cools it runs fine till it gets warm again. Maybe a pick up coil or the coil itself?

 

Good luck. I've been chasing that electrical gremlin forever!

 

I'm almost positive I found the problem. After troubleshooting various systems in the car with all checking OK, I pulled the ECM and plugged it back in hanging under the dash by the electrical harness. I got the car good and warm after driving 20 miles and then idling for 15 minutes. I then tapped on the case of the ECM with a screwdriver handle and the car stalled. I repeated this three times with the same results. I also was able to have the car stall by pressing lightly on one particular spot on the case of the ECM. I have a remanufactured Delco ECM on order. After I receive it and test it out, I'll post back with an update.

 

Well that was quick! I hope you found your problem.

 

Ok, here's an update for those that may have similar issues. The AC Delco remanufactured ECM arrived from Rock Auto yesterday afternoon, and I installed it this morning. The car fired up right away and ran perfectly. I simulated the driving distances and roads from last weekend when it acted up, and it ran perfectly with no issues the entire time. I will continue to put on some miles and will report back if it acts up again, but at this point, I'm very sure the remanufactured ECM has fixed the problem.