My 1999 BMW 328is seems to be having a wierd problem. whenever i make the engine struggle by putting the car in a low gear, the engine begins to run poorly (puttering on idle and accelerating poorly). The check engine light came on and the code came back P0305(cylinder 5 misfire). The check engine light is not always on, only when the car starts acting up(explained above).The problem is not always there, sometimes when I turn the car off it stops doing it and other times it stays. Anyone know what is specifically wrong here or had the same problem?

THanks

Swap the coil from Cylinder 5 with the coil in Cylinder 2 and see if the fault moves with the coil pack. If yes, replace that specific coil. If the fault remains with cylinder 5, look at that spark plug, and the harness connector.