We just done our rebuild...b20vtec..

the problem:
Motor revs freely with no issues when you step in the throttle, except when you hold on the throttle say at 2k rpm..it just fall flat and idle..then bounce back to 2k again..same if we try to hold the revs to 3k it just drop and jump again to 3K..

Any help????

 

Sounds like you are running an aftermarket throttle body and need to calibrate the throttle position sensor. On a B series it should be at about .48 volts at idle and about 5 volts at wide open throttle.