When starting the car up the engine idle is ok, but after a few seconds the engine revs drop and it starts misfiring. When selecting into drive and accelerating to move the car it misfires but accelerating on cruising speed this does not happen. Also when braking to give way for other vehicles(still in drive) it still misfires. When climbing it does not have power. This is really annoying and I really need your help in this matter.

Thank you