I recently replaced Bank 1 CPS on my stock 06 M35...since then, sometimes my M struggles to start. It usually occurs after I drive a little. Describing the sound: sounds like the starter is turning but takes a while for car to start....only thing i've done to car is changed rotors, brakes, battery (2 yrs ago), replaced to belts and bought a K&N filter. Is it time for more plugs (103,000 miles)?