I have a stage 2 G reg Sapphire, i ticks over high at abot 11-1200 rpm, i have cleaned the idle speed control valve & if i un plug it the engine cuts out so i dont think its the isc valve, i have turned the screw on the bottom of the throttle body (the one with a 14mm lock nut) but this doesnt alter the idle speed, what else could it be? also somimes the idle is aratic when i pull up at junctions surging up & down

please help

CheeRs Gav