Help!! 1990 GMC rich fuel mixture

I have a 1990 GMC 1/2 ton 4x4 with a 4.3 v6. 21,000 miles on it, but it has poor acceleration and fuel mileage and misses at full acceleration. It has 15 inches of vacuum new plugs & air filter, no check engine light glowing, and the injectors appear to be spraying evenly. I discovered when I unhook the PCV valve vacuum line, the engine speeds up, and then runs fine at heavy throttle with good acceleration, and power, and improved fuel economy. but has a slight miss at idle. It appears to me to be running too rich of a fuel mixture, which benefits from the extra air from the vacuum leak with the PCV hose unplugged. Any ideas what could be causing this? This truck belonged to an old man, and was hardly driven, and sat some before I got it. Could it be the throttle position sensor? Thanks for your help in solving this puzzle.

Post edited by: whiteeagle, at: 2007/05/06 04:09

engine temp sensor detects coolant temp and adjust fuel accordingly.thermostat might not bringing engine to the correct temp.wires and ignition module will cause skip.engine driven by a senior person plugs up engine cross overs with carbon remove intake and see if theirs alot of carbon egr valve my be stuck.or slowly increase engine speed .then take it on interstate open it up intermittantly blow it out.change fuel filter add injector cleaner first then do a speed run.its going to take a little work to get it back right.being stored did not do justices to the engine.break it in like a new engine.change oil and transmission fluid moisture has gotten in side from sitting.take it to the bank moisture is in their.you still might make out anyway good deal good truck rugged.