Hey guys,
My stock 2014 C63 suddenly developed a bad misfiring (shaking, flashing CEL, rpm jumping around at idle).
It has ~40k miles, spark plugs, coils and injectors were replaced ~1k miles ago, and overall maintenance is up to date.
The error codes I got are 0629 (misfires), 0633 (misfire cyl 1), 0641 (misfire cyl 4) and 0645 (misfire cyl 2), so everything on bank 1. No other codes.
From reading about similar issues, I looked into the upstream lambda sensors. My cheap scanner (icarsoft i980) shows that bank 2 lambda is around .97-.99 (seems normal) while bank 1 is constant at 1.25 (all these at idle).
Is that high lambda value indicating a bad sensor or just a correct reading of something else going wrong? Is there a way to tell from sound or exhaust if the engine is actually running rich or lean (lean would mean the sensor is likely correct, while rich would mean it's wrong and causing the computer to send way too much fuel).
I plan on replacing the sensor (and also clean the MAF), but was wondering what else could be causing this rough misfiring or if there are other parameters I should be looking at on my scanner tool to narrow down the issue.
Thanks for any help.