Registration and Posting Agreement
That should be a TBI V6. If the idle is always low cold start or hot you probably have an idle air control of IAC motor fault. That would be on the passenger rear side of the throttle body with a square 4 pin connector.
most likely a vacuum leak
What is the engine idle RPM?
Is it a V6 or straight 6?
TBI systems are very responsive and can easily mask mechanical faults and misfires. Inspect for evidence of dislodged, perforated or collapsing vacuum lines. Spray around the base of the throttle body and intake manifold with Berrymans B12 aerosol carburetor cleaner or equivalent to verify without question that there are no vacuum leaks. Place the ESC in bypass mode and check the ignition timing using a proper timing light. Temporarily remove and plug the vacuum line from the EGR valve to determine whether symptoms disappear. Perform a cylinder compression check to verify engine condition. While the spark plugs are out, inspect the insulators for cracks and check electrode wear. Disconnect the spark plug wires, one at a time, from each spark plug and the distributor cap. Use a bright flashlight to peer into the insulating boots at both ends of the wires. Look for evidence of black soot accumulation and/or greenish discoloration. Remove and inspect the distributor cap for cracks, irregularly shaped black carbon tracks, tower terminal erosion, and the condition of the carbon button protruding from the center of the cap. Verify proper fuel pressure and make sure the fuel filter is not restricted.If all of the above checks okay, remove the case hardened steel, base idle speed adjustment screw cover and completely block the IAC (idle air control) air bypass port so that no air can bypass the throttle plate. Use a proper tachometer and adjust the base idle speed to 600 RPM using the base idle speed adjustment screw. The idea is to limit minimum idle speed to 600 RPM without taking idle speed control away from the IAC. The ECM and IAC in conjunction with timing need to continue controlling the idle RPM. Try this adjustment only as a last resort.
i'd like to recommend putting a tach(even if only temporary) on it and verifying what the idle rpm is. i think some timing lights may even have a tach.These 4.3's before 92-94 VIBRATE at idle. My whole dash shakes at stoplights and i idle at about between 600-650. This is something i did not realize when i switched to this engine and it's very nerve racking.The buick v-6 also had this problem, until they got a balance shaft. Some 4.3's got a balance shaft in 92 and then ALL 4.3's got it by 95. All 90 degree v-6's have this problem----i think it has to do with whenever one cylinder is going down, two are going up. When 2 go down, 1 is coming up etc.?You say that if you give it a little throttle, all is well. EXACTLY----after 750-900 rpm on up everything is smooth. So, everything is "normal" for this engine and........You may just have to live with it.If i get another 4.3, it will likely be one of the newer LU3's with a balance shaft.