I know this is an old thread, but I am suffering every symptom to a T (almost word for word) as the guy from the original post. The difference in my case is that this was my first start up (car has sat all winter) in months. And since then I purchased the Needswings gasket kit (from valve covers up). I have torques them all to spec. I installed Robs cork gaskets (as I'm gonna be in the 20psi+ range) initially startup and actually scary. She idled so spiratic (bouncing back and forth from 1600-2400 rpms non stop) and heard a loud hissing from near the throttle body and/or y-pipe. I got scared and shut her off. This was her first start up since adding SL55 fuel pump/filter, AEM fuel regulator (set to 65psi), asp178psk, 550cc injectors, ported/coated y-pipe, ported coated SC inlet, optima redtop battery, new throttle body rubber spacer/gasket, polished intake runners, end of rail fuel pressure gauge.

The first CEL I got was 0105- "manifold absolute pressure/barometric pressure circuit" since it was the first heat up since installing new gaskets, I retorqued them down to 10th lbs. They actually were loose after torqing them initially.
I cleared the code and started her back up.

Although the hissing continued, that code didn't resurface. A different code did. She was idling higher then normal. Never below 1500rpms. She threw a 0507 code "idle control system rpm higher than expected"

When taking my y-pipe off to be sent to rob, I ended up breaking one of the clips on the AIT sensor. It felt like it was still I tight fit with one clip so I reinstalled it. I just checked it and it APPEARS to still be seated correctly. Maybe not?

Also wonder if I just need to do a throttle reset? I remember last year I backed out of a parking space, put it in drive and the pedal didn't work. I was freaking out I kept flooring it and flooring it and it would just coast. I crawled to the side of the parking lot and did a throttle reset and it was fine. I have a sprint booster installed. I don't know if this has anything to do with it as it's installed correctly. If it wasn't, it would never work to begin with.