350 TBI overfuelling
 

I have a 1991 V3500 3+3 with a 350 TBI. The problem I am having is that the truck keeps overfuelling causing the engine to stall while sitting at idle. A little background on what I've found so far- the truck will run fine at idle for about 10 minutes until the coolant reaches about 130F then stall. I removed the air filter and watched the throttle body while it was running fine and saw that the injectors were injecting a normal amount of fuel, then all of a sudden will flood the throttle body- the butterflies were closed (at idle) and fuel came up 1/8" on top of them. Of course this flooded and stalled the engine. The truck will not start normally again until i let it cool down for a couple of hours. If I want to get the engine running again with out waiting i have to remove both electrical connectors from the 2 injectors and crank the engine over- it will run for about 5 seconds as it burns off the excess fuel. i then can only hook up one of the 2 electrical connectors on the injector to get the engine to "run" although not well at all- only running with 1 of the 2 injectors. If i hook up both injectors the truck will just crank and crank- i believe because it is receiving too much fuel. i removed and cleaned the injectors with no results. I continued messing around with the truck and noticed that when the truck stalls the Idle Air Control opens all the way up- i can hear it start hissing when it opens allowing more air to bypass the butterfiles. I did not know if this was because the computer told it to open to compensate for the overfuelling or if it opened and the truck then injected more fuel to compensate for the extra air. Being at a loss i replaced the Idle Air Controller. The truck again ran perfect for 10 minutes or so until coolant temp was around 130F and stalled once again. I heard the IAC open up as it was stalling. Nothing seems to have changed so the IAC was not the issue. A little more info was that the first time I started the truck after installing the new IAC the idle was very rough but i could hear the engine almost stall, then pick back up, then almost stall, then pick back up each time getting smoother and smoother like the IAC was calibrating to get the correct idle. This makes me think that this system is operating the way it should- finding the best air/fuel ratio. however like before the truck ran perfect for 10 min then stalled. I am at a loss and have never been one to start throwing parts at something without troubleshooting. Any help would be greatly appreciated. Thanks