I have a 91 s10 4.3l. I have replaced plugs, wires, cap, rotor, and even the distribitor. I have also put in a new knock sensor, IAC valve. I have no clue to what is going on. I am ready to give up. I can’t scan due to the scanner I used will not connect to ecm and I used snap on scanner. The truck acts up intermentally. The truck acts like it has no power unless full throttle. It stalls every once in awhile. The idle is good then bad. It acted up before and then I parked it for about a year and then I drove it about 3 months with no issues. And now I’m back to square 1 with the same problems. About 1/4 throttle it goes and then acts like you aren’t hitting the throttle anymore. Then you have to give it full throttle it backfires spits and sputters then it just takes off like nothing was wrong until you let off and do it all over again. Any opinions?
My car has an automatic transmission.
Measure engine compression. Check intake vacuum to get an indirect indication of whether valves are sticking or not. Check base ignition timing and advance function and, finally, look at secondary firing patterns on an oscilloscope to determine if the issue is fuel or ignition related. If the car sat for a year, remove all the fuel injectors from the fuel rail and send them out for cleaning to a lab such as Mr. Injector (on car cleaning is useless in comparison). Partially plugged fuel injectors cause no end of problems and and might be a contributing factor in your circumstance due to the age of the vehicle and the fact that it has sat idle at one point. If you want a conclusive diagnostic from a certified mechanic just request a rough idle diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.