Doing standard tune-up things (replacing spark plugs, O2 sensor, etc...) didn't take care of the rough idle and rich exhaust error code I am getting. I'm wondering how big a vacuum leak would have to be in order to cause the MAP sensor to misread the manifold vacuum? Reading through the Code 45 info, there's not too much else in there I think would be causing my Code 45, given the fact that I have a really rough idle to go along with it. I'm thinking I have a vacuum leak somewhere, but all the lines that I can see are connected in the intake and valve covers. I'm leaning more toward the heater control vacuum lines near the firewall.
Another option I think could be possible is a leaky FPR diaphragm, or some issue with the FPR. Other than that, I don't really see a correlation. My tach is reading right, so I don't think I have an open circuit the the distributor; pretty much all of the sensors were replaced right before I bought the car, so they should be ok. Maybe the EGR valve itself, but I'm pretty sure that was replaced with the sensors. This has been and continues to bug me every time I drive the car.

 

You should probably run a vacuum gauge to the plenum and se what you have. Assuming the engine is stock and SR is about sea level, you should be about 21in/hg at idle.

There's other things which lower vacuum readings, not necessarily just a leak..i/e inginition mis-fires, timing, dead/weak cylinders, etc.