I have a 1990 or 1991( not sure[>:]) Chevy Silverado1500 EX cab EFI. It drops down to 6 or 4 cylinders and kicks backtonormal. It happens without warning and goes away. The truck might run good for a month or 2 than it starts acting up again. I managed to take a look at the engine while it was acting up once and one of the fuel injectors wasnt working right( It wouldnt spray the fuel, it would just kinda drip out)so I replaced it and it ran good for about a day or two and started acting up again. I have no Idea what is wrong and would really appreciate an answer before the dead of winter.

 

thats a feature on some new chevys ....

spark plugs? wires? I had a wire fall out of the holder and lay on the exaust, burnt through it, caused rough idle and poor performance... does it have a distributer cap?

 

Is one of your injectors restricted again? If so you need to drop & clean tank, replace strainer, replace fuel filter & blow out lines.