Engine Revs When Idling
 

Can anyone tell me why my engine when I'm idling is revving upto 2000-2500 rpm even after it shoudl be done warming up I dunno if its the Throttle Positioning Sensor or it could be somethign else on the engine btu I have a B20B egine in a 93 h/b Si And the ECU is from the 1.6 now both are B series engines but woudl this matter????

Do you have any CEL's?
check for vacuum leaks. Take some carb cleaner and spray it on all of the vacuum lines and around intake manifold gasket and throttle body gasket. If the rpms go up then the carb cleaner has entered the engine, pay close attention to where you are spraying if the rpms jump.
Also could be the Idle air control valve on the back of the intake manifold. Try checking the voltage at the TPS with a volt meter. It should be 0.5 volts at closed throttle and should slowly raise according to throttle position to 4.5 V at wide open throttle.
I would think that using a 1.6L ecu wouldn't be ideal for a 2L engine. Unless you are using a chipped p28.

i`d go with the vacumm leak

try cleaning the eac and the iac valve...... i had the same problem and it went away after cleaning.......learned this from other members on here