Hi, I have a 2009 MCS, 60k mile. I just owned this car for 1 month but the check engine light is always on. Every day when I cold start engine, the car shakes heavily. And some times the CEL is on during starting engine, and sometimes CEL is on during driving. Using a OBD II to check it, I got code P1497/2B64 (Downstream Throttle Air Leak) as well as P300-P304 (misfire), and sometimes it shows P1338/296A (intake camshaft sensor). If I eraser the codes, the codes will appear later. I went to a local BMW repair shop (not dealer) several times to check my car, they replaced four sparks, valve cover, intake camshaft position sensor, air mass meter boot, but these code are still there. They also did smoke test three times, and found nothing leaking. Besides they told me they tested the MAF sensor and it works well. Last Friday they suggested me to do a walnut blasting treatment because they think the check engine light maybe because of carbon. Is there anyone have the same situation? Is there any suggestions? Thank a lot.