Not going above 2k RPM

[Grant]

Holding the butterfly open on the TB manually under the bonnet gives the same results. I still can't understand the pops and bangs coming from the filter occasionally...
I've taken the battery off for about 5 hours (lol) to reset the ecu and it's ok at the mo. taken it round the block and it's fine. The car was quite hot earlier when it was happening. Perhaps the intake air temperature was too high?

Car is idli g a bit hight now too. Believe it to be the stepper motor, on an unrelated problem to this...