My girlfriends metro 1.4 GSi has a vibration through the throttle pedal when the revs hit just under 4,000 and again just over 4,000 apart from that the engine is smooth either side of that rev range. It is definately the engine as I tested it from under the bonnet while stationary. Could it be an un-balanced flywheel or just a slightly worn engine. It has done 85,000 with FSH. We do have a spare engine that has done 35,000. Just wondering if it's a big mechanical job (engine worn) if so could swop the engine.

The throttle cable could be touching some part of the engine, which could send vidrations down to the pedal.

Checked that and even put rubber behind pedal mount inside the car. If you rev the engine and feel it at the same time it does feel slight harsher at 4,000rpm.

Yeah my thoughts exactly - about the throttle cable.

Move the throttle cable in the engine bay when the vibration is there and see if it makes any difference.