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I have a 2002 Cadillac Deville with V8 4.6L. I was driving today and my check engine light began to flash. There was no change in the way it drove (still nice and smooth). It doesn't idle rough either. But it sputters or vibrates when I come to a stop. I ran the Codes and got a PCM P0300 code. Which I have read is a misfire detected. There are no other codes with it just that one. I hate to say but I haven't had a tune up in a while so Should I start with changing the plugs and wires and see if that stops it? Or does anyone have any other ideas.

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One quick way to tell what is happening is to look at the engine running in a dark garage. If it's plug wire or coil arcing, you should be able to see it unless it's deep in the plug wells or hidden behind the rear head. Even then you may be able to hear the arcing.

A good code reader will show hidden codes P0301-P0308 which will tell you which cylinder is missing. Freeze frame data will have a miss count on all the cylinders.

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No plug wires or exposed coils on a 2002.

You will need a GM Tech 2 or some other scanner to pinpoint which cylinder is misfiring.

Picture of a GM Tech 2 clearly showing a misfire.


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