Chevrolet Repair: Engine idles for 30 seconds and dies, vacuum leaks, vacuum leak

Question
I just replaced the engine in my 92 GMC Sierra, a 5.7 liter, it starts and runs for approximately 30 seconds or so.  Just as it seems the IAC starts to close, it dies out.  No loss of spark, fuel pressure, or injector pulse. One thing that I have noticed is that the voltage on pin #2 (lt grn returning to ecm) voltage is 4.92 volts.  Could this be the problem of this truck dying at idle.  Thanks in advance, Dan

Answer
Hi Dan,

I found this question in the question trash can.  Any of us can answer it once it is thrown away by the orginal expert.  I hope this helps.  

Are you sure the IAC is acting correctly?  Is the EGR vavle acting correctly?  Any trouble lights on dash that dont turn off?  What is the vacuum reading before it dies out?  Is the MAP sensor acting correctly?  Do you possibly have any vacuum leaks around the intake, or anywhere else?  Do you have any codes?  Was this an exact swap?  No funky year changes, or came out of a car into a truck, anything like that?  Fuel filter or air cleaner plugged?  Is the gas tank vapor locking? (try loosening gas cap)

I suspect MAP, vacuum leak, leak around air intake duct, plugged exhaust, EGR stuck open, fuel filter.  

Hope this helps.  Good luck.

C J S