During a short weekend drive in my 1989 Corvette convertable (50K miles) the engine began to run rough at idle. Pulling away from the stop light the engine smoothed out for about 10 miles and then began to shake and stumble when tryng to accelerate. The stumble when accelerating was equivilent to the one experieced on the old Carb equipped engines when they would "load up" because of a rich mixture. Eventually I could not make it up even a moderate hill and pulled over . The engine never died but idled very rough. After a very expensive flat bed tow to my garage I tried to start it up. It tried to "kick over" but no cigar. The next day it started right up, idled well for about 10 minutes, and then began the rough idle again. Shut it off and then tried to restart with no success. It did not like a hot start. after cooling off restarted and connected the Actron scanner and no codes or out of tolerance sensor conditions detected. Searched the FORUMS for my fellow suscriber experiences and ended up changing the ECU TEMP SENSOR, OXYGEN SENSOR and fuel filter. Fuel pump pressure normal. Tried disconnecting MAF sensor to default mode. Nothing changed the problem. Any suggestions from you crack L98 gearheads. Thanks

 

What kind of O2 readings you have during running condition? What voltage? Also try unplugging EGR valve to see if condition goes away. Does the car smell rich or black smoke when this happens? What is your TPS voltage reading @ idle and is it rock solid?

 

Replaced O2 sensor, unplugged EGR and the TPS is about 2.3 volt. No black smoke or "rich" smell. No change. Any more suggestions? Much Thanks

 

TPS is way high. Should be around a half volt @ idle. That is why your car is running rich. ECM thinks you have throttle half way open @ idle. Look at your O2 voltage readings, probably hovering around .8 volt to 1 volt. Replace TPS with a good quality A/C delco one. They are marginally ajustable. 3 wires to sensor, 1 is 5v reference, 1 is signal return (the .5 volt signal), the other is sensor ground. The reason it runs good for 10 minutes, it still is in open loop and using fixed readings. [8D]