2000 Lesabre P0303 Trouble Code

The other day the vehicle started and ran rough. Turned off and restarted, ran ok and has been running that way since. Pulled codes and found P0303 was stored (Intermittent Firing on Cylinder 3.0 Any ideas what may be going
on? Had the vehicle recently serviced under the Dex-Cool campaign. Any suggestion what to look for? Vehicle has 54,000 miles. Thanks.
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Well the first thing to do is check the plug and wire on cylinder 3.

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