Chevrolet Repair: 88 chevy tbi blows black smoke, scan tool, egr valve

Question
Truck C2500 with TBI 350cu in and 132,000 miles.
Starts, runs and drives fine when cold and as long as you keep driving runs fine.  The check engine light comes on sometimes after driving 5-10 miles.  
Problem - Once truck is warmed up and you shut it off for 15-20 minutes and then start it up it blows black smoke out of exhaust and I have to hold a fast idle for about a minute to keep it running until it clears up. Will then run fine.  EGR valve was replaced about 6 months ago but problem started about 2 months ago.

Answer
Hi Dennis, It would be nice to see the data from a scan tool on this one. I'm thinking a bad coolant sensor is the problem here. If the coolant sensor is telling the ECM that the engine is like very cold (20 degrees) it will make it run very rich. This would be the first place to look. Let me know what happens.


Mark