So, lately my check engine light has been coming on with codes P0300 (Random/Multiple Misfire detected) and P0301 (Cylinder Number 1 Misfire Detected). The car sputters and idles a little rough when it does this and my DSC light illuminates. If I shut the car off and start it back up, the DSC light stays off. Car drives just fine regardless.

I thought maybe the spark plugs plugs have never been changed. So new NGK plugs and wires installed. I did notice black build up on the connectors of the ignition coil. I cleaned them up, but the connector for cylinder three was darker than the others. Don’t think that makes a huge difference, but the problem continues. Next up is to just replace the ignition coil and see if that solves the problem, but curious if anyone else has had this issue, and what could be my real problem. The DSC light coming on is what is throwing me off...

I have 06 MSC that I bought recently with 63,000 miles. Third day after I had it the exact same thing happens. Same codes, same symptoms. It would start and immediately sputter and run on three cylinders. Shut it off and restart and it was fine. I checked the coil and wires. Did the swap plug and wire routine. Even pulled the number 1 cylinder wire, while it was sputtering and had great spark all the way out of the whole. Checked injector connections, plugs are correct for car and look brand new.

I finally checked the fuel pressure. Key on pressure would come up to 30-40 psi, but then immediately bleed off to zero within 10 seconds. Bad check valve in pump. So until I replace the fuel pump I turn the key to run and wait two or three seconds then start. Try what I did before you throw any more money at it.

I’m not 100% sure what I did, but the problem seems to have resolved itself. Haven’t thrown those codes for a while now. I ended up changing out the plugs, wires, still did it. Changed out the ignition coil and added some fuel system cleaner in the gas on two fill ups. Seems to be running fine now other than a vacuum issue now.