Strange problem

Having resolved the issues with boost another has started, had a issue with hanging revs over last fee days. Car will suddenly sit at 2000rpm for no reason, pulling up to park and boom ! revs rise. Not always though. Checked pcv and suprise its sucking like a mother !!, put my copy pcv on and was resolved. But sat in traffic last night it started again, temp gauge sat at 90 but revs went upto 1600, then when i parked up it would not go below 1100. Normaly blipping the throttle stops it but not this time, only seems to be when hot though