1999 Fiat Punto engine problem

the car runs fine throughout the rev range until it gets up to normal running temperature, when it gets to this point it idles fine and if u build the revs slowly this is also fine, but if u hit the accelerator to rev up quickly the car struggles to build revs, stutters and sometimes backfires or cuts out. I've changed the throttle body with both sensors (throttle position sensor + auto chalk) and this has made no difference. I would appreciate any info or suggestions, thanks.