I have a 91 GMC 1500 pickup with a TBI 350. It has 128,000 miles and has never given me a problem until now. The Tbi is dumping gas in at idle and is just flooding it out. It runs great above 1500 rpm's. It happened all of a sudden. The only engine code I got was MAP sensor. I replaced it with no change. So I replaced the injectors, regulator,mounting gasket, TPS, plugs, even the ECM with no change. Next is the coolant sensor. I am at a lose. It is only showing 5 inch of vacuum at idle, not enough for the map sensor to work. When we put a vac. of 18 it idles great. With the engine running it sounds like it has a big vac. leak at the throttle body, but we have checked everything that I can think of. ANY help would be great. Thanks Tom
idle air solenoid? have you traced the vac. line from the MAP to it's source? sometimes O2 sensors give problems but don't give a code. is your EGR stuck open?
I replaced the iac and checked the vac. line and it isn't clogged. My next step is to replace the egr. It is only a few months old.
Yes, replace the coolant sensor. My 4.3 Blazer was doing the same thing your truck was doing. I put my OTC monitor on it and the coolant temp sensor was reading -40 degrees on a 90 degree day. This caused the computer to pour more fuel into the motor flooding it out. I figured this out after replacing the regulator and fuel pump.
