Where to start, ok I change valve cover gasket (bmw) do to oil was leaking
on plugs. I fixed that and put in new bmw plugs $$, but still have poor engine performance. going up hill no power above 25mph engine & valves rattles. down hill good to go. I'm looking @ the fuel filter now. My cats rattle which is out do that effect it, also do the coils cause it? 168K mi on it PLEASE HELP.