95 GT throwing code 312

I recently purchased a 95 GT that is bone stock as far as the engine goes. The idle was rought and it was throwing lean codes for both banks, but I've cleared the codes up with a new MAF sensor. It runs a lot better, but now the idle is high (even after resetting the idle) and it still has a slight misfire at low RPM's. I've checked everything for vacuum leaks and can't find any. Now it finally started throwing a code 312 when I do a KOER test. This apparently mean the AIR system isn't being diverted. Would this cause the high idle/misfire? Also, how the heck does one go about fixing this?

Thanks in advance!

Sounds like good advise. I've already doused the intake/throttle body and engine compartment vacuum hoses in carb cleaner, but I guess the next step is opening the fender and working from there. I'm going to do this tonight, so hopefully I can trace the problem. This has been driving me nuts for 3 months now!