P0300 Code and Rough Idling

[bedwar2]

I have a 1997 Malibu (with 152,000+ miles) and lately noticed that the car idles roughly which is especially notacible when at a complete stop. It feels like the car may stall but never does. Recently the check engine light came on and a code reading at Advanced Auto Parts revealed that it was a P0300 code which is random cylinder misfires. I did a secondary resistance test on the ignition coils and tested voltage to EGR valve and those tests were successful. Wires look good as well and both plugs/wires were replaced around 40,000-50,000 miles ago.

Any suggestions as to what can be causing the problem and/or other diagnostics I could perform?

Thank you in advance for any help!

[rhandwor]

I would pull the plugs and look at them hunting for a small crack and proper gap. At 40,000 they should be changed if non platinum. Use an ohm meter and check each wire moving the wires with the meter on them. This way if you have a small break it will show up. Listen to the injectors with a stethoscope to determine if they sound the same.

[bedwar2]

Thanks for the reply. I was told it is unlikely it is plugs or wires since code is random misfires and not specific to a cylinder. Could it be EGR Valve is bad or a vacuum leak? Not sure how to test those possibilities. How about Idle Air Control valve? I'm just thinking these because it is random/multiple cylinder misfires.

Thanks

[rhandwor]

Without proper tools at least check the wires with an ohm meter and wiggle especially the spark plug end. They can get small cracks in the carbon and work some times and not at other times. Each coil fires twice during the cycle and one bad wire can effect two cylinders. Wiggle the wires to the module which advance will test free if you take it in. A bad connection will cause a misfire. Inspect each plug for worn or broken connections. I would clean the IAC valve and throttle housing.

[KD8AYL]

I have a similar problem. I have a 97 Malibu with 245,000 miles. While driving the engine just shut down and would not restart (I was not present) When I got the vehicle it would start and run rough for a few seconds and then die. Engine code P0300 was displayed 2 times.
I have yet to get the engine to restart and run. Sounds like the likly suspect is the plugs and wires corret?