was just driving home came off a roundabout gave it some boost in 2nd gear and the car started knocking so backed off and pulled over. car is missfiring and when revved a knocking/tapping noise comes from what seems like the rocker cover. managed to limp home but its too dark to start stripping it down to have a look anyone got any ideas?? the knocking/tapping only happens when accelerating nothing when coming back down through the gears.