My car has Cosworth blue injectors and when on the road sounds and goes brilliantly, however no matter how much i play with the throttle pot i can not get it to idle properly, it seems to hunt to about 2-2.5k revs then drop to almost nothing then recover to normal or stall. The car seems to run at it's best (on the M4 test way anyway

Please help!!!!!
Confused as usual
Jon