Car shudders at 2kRPM Options

[cyborg]

Hey, got a problem with my celica, if i hold the car at a steady rev of about 2k RPM the car judders back and forth like its about to stall, but doesn't and just judders violently (similar effect to if you tap the accelerator on and off) My friend suggested its the throttle position sensor, think that sounds right?

I've recently changed distrubution cap, rotary arm, spark plugs and HT leads. Problem persists, and can give a bad flat spot when reving.