smikey

Girlfriend has 2001 ML 320. Got fuel at 7-11 and starting running rough. Engine code P0300 (random misfire) Dumped fuel injector cleaner in, no change. Changed spark plugs and cleaned MAF Sensor. Cleared diagnostic codes and restarted engine. Same code comes up again. What's next? Wires? Any suggestions or insights would be helpful. I'm fairly mechanically inclined with DIY stuff, but I've always worked on other types of vehicles (Honda Toyota. Just not familiar with Mercedes. Thanks in advance

smikey

Should I try to siphon the fuel off and replace with different fuel? It seems like the problem started after picking up that load of fuel. Not saying that the problem wasn't going to occur anyways, but that is when it started

gsfent

Find some winter products that absorb water in fuel. If you have a bad load of fuel, it is either sediment or water. You could dump at least half the tank and replace with fresh, although without testing the fuel itself, hard to know if that is your issue.

Don't recall the product name, but they are always available in the wintertime. Add a can and see if that helps.

Other things to check for are leaking or broken vacuum hoses. If the car only idles poorly, but runs ok, less likely it is fuel and more likely vacuum hose.

Other possibilities bad CPS, bad spark plug, bad coil. Does the misfire code isolate a particular cylinder?

Regards,
Jerry

smikey

need to get in and check vaccuum lines today. code was P0300- random misfires detected. Dropped Sea foam in the gas tank with no change. Didn't try adding sea foam in through the intake yet. Put new plugs in and had no change. Just trying to go through the easier fixes before trying something more expensive.