Before you replace anything, I have a thought, have you tried resetting any adaptations to the fuel injection? I had this issue on my e36. Like what ard said. For me I had a vacuum leak and when I fixed it, the car was running super rich and bogging down. It did not lean the fuel back out right away after the problem was gone. Disconnecting the battery for some time let the ECU clear the memory or something and go back to default. Started the car and was perfect from then.
May not be anything like this, but something free to try.


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