I have a 1984 gmc truck that was originally a 6.2 diesel and was converted to a 350 from a 1991 or 1992 (i think) truck. It has the throttle body setup and has worked fine until lately. First it started idling high a couple of minutes after startup but would fluctuate between high and normal idle while driving. Then it developed the problem of wanting to sputter and kinda miss a little when you take your foot off the gas and press again (while driving). Now it has begun to be EXTREMELY hard to start. Its almost like it's flooded. It won't fire at all until you hold the pedal to the floor while turning over and after SEVERAL seconds it will try to fire but you have to work the accelerator back and forth between on-the-floor and almost-on-the-floor for awhile and with luck it'll sputter to life. Then it has a tendency to die once you put it in Drive and the cycle repeats. It seems that if you immediately try to start it back it will fire off more easily than if you let it sit for a minute or two before trying it. This was my grandpa's truck and I'm resurrecting it to keep it from wasting away in the barn. It sat for about 8 years before i dug it out and got it going and then only had the idling and slight miss problem. The tranny went bad and it sat again for a year. I just installed the new trans and now am facing the starting/dying issues along with the original problems. When I moved it to the shop to take out the bad trans , I recall it being hard to start but I assumed it was from sitting so long, guess I was wrong. Any help or advice is greatly appreciated

 

Have you checked the timing, wires and distributor? Does it crank hard? Sounds to me like a timing problem.

 

check all ignition components. also look for vacuum leaks. check every single vacuum line at, on, around motor.

 

Fixed it ! It was the Coolant Temp Sensor next to the water neck/thermostat. Doesn't techology make you want to pull your hair out sometimes? HAHA ! Thanks for the advice everybody

 

Glad that you found the problem, I thought that may be a possible cause but it didn't come to mind right away. I had a similar problem a couple years ago.