What is a normal range for engine vacuum at idle? My scanner is saying there is 9" which seems low to me. There is a slight driveability issue with there being a lag and hesitation at part throttle when trying to accelerate slowly. A heavier foot gives normal throttle response. Based on getting an EGR code a number of times, I did just replace the EGR valve with no change in the vacuum reading.

 

it suppose to be like 18-20" of vacuum. Make sure you are reading the Units on the scanner right, tho. Some scanner shows it in Kpa, some shows in PSI, number will be different if unit is different.
What does it read with the Engine OFF. tho? doing it drop to 0 inch or 30 inch?

Well, disconnect the MAP sensor, and test drive the vehicle, see if you get any different. MAP sensor is what's reading the Vacuum, but if you disconnect it, the Computer will substitute it with "Calculated" Vacuum. If MAP is faulty, it might run better with a Calculated MAP instead of Actual.

 

The scanner reads 8.9" of mercury. I'm a novice when it comes to interpreting the real time data. I checked last night on the highway and the LTFT was essentially 0 but this morning at idle and a cold engine, it was reading 6.7%.

 

well, Fuel trim is fine. as long as it doesnt go pass 20%
Some cars reads Vacuum in a inversed way. Supposely with engine Off, Atmospheric pressure should read 0", and complete vacuum is 29.9".
However, if the vehicle is inversed, engine off, it will read 29.9, and complete vacuum is 0". and if you take 29.9 - 8.9 = 21" vacuum, which is correct.

So, if scanner reads 29.9"ish with key on engine off, your car is reading Inversed, and 8.9" vacuum is correct. Your problem lays somewhere else.

 

With the engine off, the MAP reading is 29.2" I tried disconnecting the vacuum sources for the power brake booster, PCV, cruise control and evap system with no change in the vacuum reading(the ports were taped).
So, it would seem that if the reading is indeed low, the leak must be coming from the plenum/throttle body area.