I ride a 300i downtown when I put a iridium plug in I had no change in rpm. at idle, but it sure ran smoother,. is it from more miles , and breaking in, or just the plug, it is still getting smoother it seems, and im over 33.000 km. thats just over 20,600 miles,. something opened up in the muffler,. and it makes a little more noise,. sounds good to me, it could be my hearing is getting better, ha ha,. I dont ride with my hearing aids,. the wind would drive me nuts, I tryed it once and that was enough,