New car, few questions with issues.

[cdnmmaguy]

I just bought a 10AE and I got a good deal on it, and theres a few things that need to be addressed.
First off, the throttle is sticking, it wont drop down to an idle and raises while im driving.
Second, I believe its running REALLY rich, it backfires ALOT lol
Third, the car is modded quite a bit, and last night I was hitting almost 14-15psi consistantly, today, just 7.

Pretty much all these problems just started within the last 12hrs or so, I bought the car yesterday out of town and drove it home with zero problems.
Im not sure if this makes a difference, but theres a leak in the exhaust manifold gasket and it sounds like a tractor haha

If you guys could help a newbie out, id appreciate it, or at least point me in the right direction, ive booked it into a shop to get the other minor problems fixed, but thats not for 2 weeks

Thanks