'97 Firebird Misfiring...

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'97 Firebird, automatic V6. The check engine light was on when I got in the car after I had just returned home for winter break, so I took it down to Schuck's to get the codes read. It came back with a P030X code, defined as "6th cylinder misfire" by the code reader. I checked the plug wire and plug for that cylinder, and they appear to be fine.

The actual problem is that the car jerks while attempting to accelerate in the 3000-4500 rpm range. Once outside that range (takes a while to get through because of the fluctuation in rpms) acceleration becomes smooth again. The misfiring doesn't occur in first gear, revealed by manually shifting the transmission.

Little note about the check engine light: The light turned off after getting the codes read (presumably because the dude cleared the code) and stayed off for a few days. Under heavy acceleration while avoiding a collision with an oblivious soccer mom, the light turned itself back on, but later in that same drive, turned off again. It has stayed off since then, but the problem persists.

Fix this and you're a god.

If the ignition system checks out ok, then I'd move on and chekc the fuel injector out.

Was it indeed a P0306 code?

The light will come on when the problem is detected for a set time frame, and will shut off when the problem no longer occurs for another period.