Last night, while idling in a parking lot and waiting for my daughter to get out of her volleyball practice, her Mini started idling roughly and the SES light came on - it was blinking for a few seconds, and then went solid. I had - fortunately - just picked up a Foxwell NT510 off of FB Marketplace (I needed something to do while she was in practice ), so I was able to read the code and it came up as P0302. The car was still running, just stumbling a bit, so we left for home. All the way home, the stumbling was present, until we exited the highway and came to stop on the off-ramp - then the stumbling stopped! It ran normally the last 3 miles of our drive (the SES remained lit solid - this is expected behavior).

I've been researching other threads on the P0302 misfire and have compiled a list of things to try and check:

• Check the spark plugs (These have been replaced in the last 5k miles. I will pull the #2 plug and check its condition.)
• Check the spark plug wire and coil connections (It doesn't seem like it is a coil issue, as others have said that the cylinders/plugs are paired with the coil, so another cylinder would be misfiring, as well, if it was the coil)
• Replace the in-tank fuel filter (This has likely never been done...we've only had the car since last June and 154k miles).
• Compression test (Compare the compression readings across all cylinders)
• Leak Down test (If there is a wonky reading in the compression test)
• Fuel Injector O-rings (these are likely original, too)
• Fuel Injector

I'll document my findings here. Thanks for any input.

When I started the Mini this morning, it started and idled/ran fine - no stumbling. I shut off the car, cleared the DTC and restarted the car and the SES remained off. So, we'll see if it happens again (or more and more).

Oh, and the Foxwell confirmed that the ABS fault we have is due to a bad LF wheel speed sensor. That is already ordered and will be replaced.

 

Sounds like it could be a dirty injector.

 

Is she using Top Tier top octane fuel? I had to learn the Top Tier lesson the hard way several years ago with similar issues.
And just to help keep the fuel system healthy add a can of BG-44K to the tank every 4 or 5 months.

https://www.toptiergas.com/licensed-brands/

 

Thanks for the tips. We do use premium fuel, typically from Costco (which is on the Top Tier list).

I did add a can of fuel system/injector cleaner today. We'll be driving it more over the coming days.

I am leaning towards it being an injector issue, too.

 

Today's update: put about 40 miles on the Mini driving around today (trying to work some of that fuel system/injector cleaner through)...it didn't stumble or have issues.

 

LAtest update: there has been no repeat of the misfire condition in the last few weeks (we drove another 250 miles or so on the car, since then).