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1992 2500 Chevy Runs Rough Occasionally

My pickup runs smooth 95% of the time. It runs rough at red lights and when pulling away from stops. It seems to happen more when the A/C is on.

Plugs and filter changes etc. up to date?

I would:

  1. Pour a bottle of Chevron Techron in a tank of gas. Two with a big tank.
  2. Look for a vacuum leak.
  3. Do a compression test.

One thing I have found on these old throttle body injected pickups that will cause your exact symptoms is the vacuum port for the MAP sensor on the TB gets gummed up causing the MAP sensor readings to be askew.

Thanks for the comments. I took some carburetor cleaner and sprayed out the MAP sensor vacuum port. Also the throttle body and a few other vacuum ports. It seems to have fixed the problem.