FullTorque

I'm looking for info on PO300 which is random cylinder misfire. I also show 301, 302, 303, 307, 308, and 309. The dealer just installed new plugs, motor mounts, air cleaners and I tuned it to 600 hp. Any ideas what might be causing these codes before I take it the dealer. Car is 2004 SL600 with 58K miles. It runs rough only once and a while it is not constant.

sifis

A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

FullTorque

Thanks, I've learned those details since this started. The dealer found that both ignition coils were putting out less than required voltage so they have replaced them. ($3300.00)I'll pick it up tomorrow and see how it does.

pzsfive

Hi. Did you ever figure out what was causing the misifres? I have the same problem with my S500 but only when I floor it. Any help would work. All new plugs etc. pretty irritating.