Car troubles =[

[joel w]

The turbo is your back pressure...You could disconnect the downpipe and it will run fine.

It can be lots of things causing this, I would check for codes and timing and look for leaks in the IC pipes, couplers, IC, 300 pipe and intake.. here is a how to leak detector.
http://www.vfaq.com/mods/ICtester.html

Here is a TSRM.. codes are under EFI
http://www.cygnusx1.net/supra/library/TSRM/

Theweezle is correct in saying you can still hit 7psi with a large boost leak. The turbo will just have to work harder and pull more air through the AFM to maintain pressure. This excess air through the AFM will trick the ecu into thinking your flowing more air into the motor. The ECU will add more fuel to compensate, causing a rich scenario.