Yes if you hammer it then stop at say a junction or something it will stall, but he said it definately did it before the dump valve was fitted because he booked it in at the garage i work at and ive check the computer and we fitted an idle speed contol valve, which obviously hasnt work!
I'll try that though, we has the battery off when we fitted the K&N but I reved it up as soon as I started it ha ha!
Thanks guys!