You really shouldn't have screwed with trying to manually adjust the idle.... it's computer controlled and unless you know exactly what you're doing you can make the diagnosis of the REAL problem even harder.
Start with checking for diagnostic codes:
http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx
Then check for vacuum leaks.
Is the stock blow off valve still installed and correctly routed?
You haven't tried to clean the air flow meter I hope.