I BOUGHT A 92 SONOMA TRUCK WITH A 4.3 VORTEC ENGINE FROM MY FRIEND.IT HAS ROUGH IDLED FOR THE LAST 8 YEARS FOR HIM. I HAVE HAD IT TUNED , WIRES , EVERYTHING. HE HAD IT TO SEVERAL MECHANICS AND IT STILL ROUGH IDLED. I JUST TALKED WITH SOMEONE WHO HAS A 91 SONOMA AND HE HAS THE SAME PROBLEM! HELP!
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You must have an egr valve for this engine to work.Sounds like you are getting oil blow-by combustion causing carbon in the exhaust which may do due to a faulty crankcase ventilation valve, bad piston rings, etc. Whatever the cause, oil combustion produces the carbon, and you will need to fix that.
Hello I have a 1995 Sonoma 4.3 with 150.000 on her and she ran great tell last week went to pick up a lite trailer and dove it home no problem drove it all day after that. The parked it running fine and next morning it won't hold a idle but clears up at 3000 RPM runs fine drop in gear and it won't stay running??? Cleaned TBI and there was a new fuel pump and filter put on it less them 7.000 miles ago. Found vacuum leak on the booster to manifold fix that still runs like it is misfiring??? Any help would be great thanks no check engine light on.
Check for vacumn leaks ! Idle air compensator? clean throttle valve oppenings and air port opening,do you have check engine lite on,check EGR valve? Dirty fuel injectors ,bad pressure regulator?Check fuel pressure at fuel rail,at idle !
Try a full tune up.. get Bosch platnium+4 spark plugs and Acel wires, do the fuel filter and air filter(i suggest K&N) buy some fuel injector cleaner or use Marvel Mystery oil. The ECU could e gone but hard to diagnose if the car needs a tune up.
your probably feeling a rough idle of the engine. need a tune up?
in park the engine is not loaded down, just idling at a low rpm=rough
in drive with brake on you have put some load on motor also at low rpm=rough
in drive on the road engine is at higher rpm, = smoother
generally 4 cylinder motors idle a bit rough, especially if one spark plug is not firing right or fouled or one bad spark plug wire. tune up may fix it. if it is not stumbling real bad or stalling then you can live with it.