I have an '03 mini cooper and have been getting OBD code P0301 consistently. I have had previous reads of low compression in the 1st cylinder as well. Usually it misfires while idle, SES light flashes, and then it goes back to normal after a few miles. This past week, I have been having issues of misfiring while accelerating.
We have swapped out the fuel injectors, checked the coils, and the code remains the same. Changing the plugs next. Any thoughts?

 

Have you done a compression test at all? And if so what was the reading on each cylinder?

 

Hate to say it...but You might have a valve issue....

 

Compression test showed low in the 1st cylinder. I apologize, I don't have the numbers here, but I believe the 1st cylinder was in the low 120s.

 

I guess you could change your plugs and go from there..I would do all the basic and easy things first like you have. But if you can do a leak down test on cylinder #1. see what you get. If its in the 120s see if it holds it there. But also compare all cylinders when doing this. If you notice that cylinder #1 does lose its psi rather quickly then one could say its likely a bad valve in that cylinder just like ZippyNH has suggested. But makes sure you compare this across all the cylinders to make sure your getting accurate info from the leak down test. Also when you change your plugs compare them and see if cylinder #1 shows any signs of something wrong or see if its burning the same. good luck !

 

Alright, will do! Thanks!

 

FYI, compression/leakdown tests need to be done when the engine is warm and has reached operating temperature...if the tests are ran on a cold engine it won't (lower than actual numbers) be accurate because an engine is built to spec around when its warm because thats when the metal expands..