Ive checked again for any vacuum leaks, and ther definately isnt any.

I have a 7.?lb steel flywheel and skunk 2 stage 2 cams running on a stock ecu at the moment, that couldnt be the cause could it??

Ive got my hands on another 'good' IACV, so i'll fit that just incase its a intermittant faulty unit.