Bad Idle and no throttle response

ENGINE/DRIVABILITY:

Year/Make/Model: 2008 Mazdaspeed3
Mileage: 144k
Location: Green Bay, WI
Concern/Story: I recently bought the car and it had a misfire with codes P0300 and P0303. It only misfired at high rpms, so I took it easy and drove it home (an hour) on the highway. Once I got on the exit near my home, the car had barely any acceleration response and it had to be limped home. The previous owner changed the coilpacks, but it didn't fix the misfire. However, after I had done my recent repairs(see below), it no longer misfires, but the car will idle erratically and stall itself out. If I press on the gas the car doesn't do anything. I read that the IAC valve could have been gunked up and that may be the issue. However, I can't find any images or the location of it. Any ideas on what could be the issue?
DTC's: Currently has codes P0138, P0463
Modifications: Injen Intake, AEM 340LPH Fuel Pump
ECU/Tuning Software: Stock ECU, previous owner did have an an accessport but it didn't come with the car.
Tuner: Not that I know of.
Is the concern intermittent? No
Can you duplicate the concern? Yes
Recent Repairs: New fuel pump (AEM 340LPH), New High Pressure Fuel line(old one was leaking fuel)

 

With the car running does the throttle body open when you move the pedal?