I HAVE A 94 GMC JIMMY WITH VORTEC 4.3 IT SHOWS NO CODES AND THE SERVICE
ENGINE LIGHT HAS NOT COME ON.THE PROBLEM IS WHEN YOU TRY TO START THE
ENGINE CRANKS OVER AND FINALLY FIRES BUT RUN REALLY SLUGGISH FOR A FEW
SECONDS AND THEN GOES TO FAST IDLE AS IT SHOULD THEN HAS A HEAVY FUEL
SMELL LIKE IT WAS FLOODED THEN IT RUNS FINE TILL YOU TRY TO START IT
AGAIN.I HAVE CHANGED THE EGR VALVE,TPS,COIL,IDLE AIR,FROM ANOTHER VORTEC
ENGINE, THANKS FOR ANY HELP!!!!

To cheat and not actually have to pull the whole upper plenum. remove
the vortec cover opn top, there is a round hockey puck looking thing
underneath (it's the IMTV) if you pull that out and shine a real bright
flashlight in there you can look for any sign of cleanliness. If you
see shiny and clean then your fuel cpi or line is leaking

http://www.samscars.com/mage7.html
the site above will show you what you are looking for

mike