Bests & Worsts Reviews from Amazon

I used it on my 2003 BMW 325 (with 100k miles on board) this weekend, to try to get rid of some rough idle issues. I followed the instructions to the letter; someone kept the RPM at 1500 while I used the spray for about 2 minutes. During this period, nothing happened, the engine behaved normally. Then, I left the cleaner do its job for 5 minutes. When I restarted the engine, it got really scary: a plume of grey smoke inundated the yard, and the engine was barely running. The Service Engine Soon" light was on. I drove it on some side streets for about 5 minutes (kept it in manual mode, to run it at high RPM, as instructed) and then drove it on the highway for about 10 minutes. Even before reaching the highway, the engine started running really smooth, and the "Service Engine Soon" light went off. While on the highway, I noticed how smooth the engine was running now, and I could feel more power under the hood (hard to quantify, but I would say about 10% better). The next day I noticed that, even when the engine was cold, the idle would be really smooth, barely feeling it in the steering wheel. Gas mileage went up (the instantaneous onboard indicator show around 35-40mgp @ 65mph - on cruise control). As a conclusion, I would say that it's a very effective treatment, but not for the faint of heart...