I am not real in tune to these motors, yet, but it doesn't sound like by pulling a vaccuum hose would rule it to be too much fuel. If it was running rich at idle the fumes would be enough to most likely burn your eyes around the rear of the truck. When you pull a vaccuum line you are simply taking a load off of the engine, That is why it is idling up. However I am not sure what your problem may be. Someone will ring in that has had this problem before. Good luck