1999 Chevrolet Silverado Service engine light keeps coming.

Service light light keeps coming on after serveral repair have been done to the engine.
Replace intake and out take sensors.
Replaced the air line.
The computer say it s multi miss fires
Fuel pump reads about 48
Clean the carburetor with cleaner, placed fuel cleaners in the engine.
It run great on the high way, but stopped at a light runs rough. The light usually come on at the stop
Light. It has come on for away and gone away for way at times.
Can you any other suggestion on the problem? The mechanic does not think it the spark plugs because of multi miss fires.