Cadillac Repair: 1996 4.6 NorthStar Intake Manifold Vacuum Leak, fuel pressure regulator, vacuum leak

Question
My mileage has begun to drop. The engine seems to run fine. My e-brake doesn't release automatically. When I drive up a steep grade at speed over 60 my air cond shuts down and all the air is diverted to the defroster vents until I release the throttle then all goes back to normal.

I have checked over the engine and everything seems fine. The only thing I notice is on the front of the intake manifold there is a round insert that has a vacuum port on it. It seems like this round insert is loose. Is this supposed to be loose? I can't find any description of the intake manifold anywhere.

Thanks

Answer
Hi Rod, Somewhere you have a vacuum leak. There is a reserve tank in the engine compartment that may be leaking or the hose came off. A vacuum hose under the dash or engine compartment could be leaking as could the fuel pressure regulator diaphram. Run the engine and shut it off and then remove the vacuum line from the pressure reguilatoer and see if fuel is getting into the line. Use your ears and listen for hissing while the engine is running or trace the circuits with a vacuum gage to see where you get vacuum. then look at the lines etc. for a leak. Hope that helps. Bill