map sensor problems

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i picked this car up from a friend who replaced the engine with another one just like it. i had to redo the entire vaccum system he had it all messed up according to the diagram and that didnt help it. when i plug the map sensor up it seems to lean out some but the idle goes up to about 2k. i checked the map sensor voltage i have 5v at the cpu and 5 at the plug under atmospheric pressure when i simply plug the map back in the voltage drops to 3 volts. is that right? the computer is kicking the