P0305 Cylinder Misfire
 

Afternoon Gents.

2009 255K Miles
R2C Intakes
Art pipes/FI exhaust
Oil change 5K ago

Filled Z from empty to full Thursday morning on way to office. Traffic of course ground to a halt, and I immediately noticed my exhaust note discernibly changed, accompanied by an SES light. I was only a few miles away from office and plugged my OBDII scanner in and obtained the P0305. Rough idle, lots of vibration, some extra fuel smell, but made it back home.

Checked plugs Friday, #5 was significantly darker than the rest. Figured new plugs would do the trick so I put a new set of NGKs in today. Also cleaned the throttle bodies as they definitely needed it. Additionally, tested coil packs with a multimeter and all appeared fine for resistance.

Reassembled everything. Rough idle over 1K still. Ran through all of motorvates videos for after cleaning throttle bodies, cleared codes, and drove for 10 minutes. At this time, the lovely P0300 popped up. However, after running through the idle relearn and clearing codes only P0305 remains. Idle is back down near 700, but definitely not running right. Feels jittery especially when placing in drive.

Any further thoughts for the culprit? I know this one can be so many things. Was considering swapping the coil pack with another just to see if the misfire moved cylinders.

P0305 Cylinder Misfire
 

Swap the coil packs between cylinders. If no change, swap the injectors between cylinders. Given the mileage on your car, you could have a failing injector or it could be clogged up

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Going to swap coil packs tomorrow after work when I’ve got daylight. If issue doesn’t change from cylinder 5 I’ll try a fuel injector swap next.

Most likely you got bad fuel in there considering it happened right after refuel. I'd get a fuel sample and check it out for water content.

Welp. I certainly believe the culprit is the coil. I swapped it to #3, cleared codes, and immediately got a #3 misfire now. Ordered a replacement coil pack to swap in.

I do appreciate the help.

Resistance checks for coils is a complete waste of time. Can’t tell you how many I’ve seen in the past pass a resistance check and still not fire under load. Best to either swap coils or even better buy yourself a HEI coil tester, the kind that have no center electrode with the housing that clips to ground is the best. If the coil can fire that then you’re good, and you’ll get a nice audible indicator as well as visual. They’re cheap and save you time swapping coils and test driving.