2002 XJ8 4.0 Engine Misfire. Need help diagnosing.
 

Hey guys, new to the forum. I have a 2002 XJ8 with the 4.0 (not supercharged). Lately I've been occasionally getting a check engine light with the codes P0300, P0305, P0306, P0307, and P0308. Also an intermittent Restricted Performance mode.

The car will run fine once it's moving, but idle at stops is extremely rough around 600 RPM and that's always where it'll throw the misfire codes. I thought it might be that one of the ignition coils had gone bad on the left side of the engine (since that's where 5-8 are), but I can unplug each ignition coil on that side with no change in the rough idle for better or worse. Even with all 4 ignition coils on that side unplugged at the same time (5-8), the car runs no worse and even seemed to run a little better. There's no evidence of any oil/fuel/other fluid leaking in the engine compartment.

Any guidance or help would be greatly appreciated. Thanks!

If I were a betting man, I would wager that your secondary tensioner is bad on the left bank and you have jumped a sprocket. Almost always the case when each cylinder misfires on one bank. You are out of time on the left back. Next, you will lose an engine. Don't drive it until you have checked your tensioners. Huge number of threads to tell you how.

Check this one, this page: Default How Do I Know If My Tensioners Are Broken? #11.

And if the tensioner has failed on the left side, it will soon fail on the right.

Do a check over on the XK8 side of the forum: one their members had the exact same problem -- I was positive it was a timing problem as noted, supra -- he cleaned all four coils and the problem was solved. I wouldn't bet that is your problem.

What would be useful would be to add your location and your car's info to your signature.

And please visit the new member area and introduce yourself when you have time:

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