That could be the problem, while the platinum plugs are advertised as super-duper, gee-whiz, and all that, I don't believe they are factory spec, and for some reason non-factory spec plugs just lead to trouble in BMW engines, at least in the 6-cylinder series, and I believe that holds true for the 4-cylinders as well. So spending $10-$12 for four correct plugs might be a cheap solution to your driveability problem.