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Very rough idle on start with misfires in one bank only

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Good morning, here is my challenge with my 2004 high mileage Cayenne Turbo: on initial startup, I get a very rough idle that will settle after a minute or two, after the typical start-up cycle, although it will remain a bit rough afterward as well. I ran my codes and came back with these: 


P0199 - engine oil sensor (more on that in a moment)

P0021  - cam position timing over advanced or system performance B2

P0431 - catalyst system efficiency below threshold bank 2

Plus misfires on 1, 3, 4 

P0446 - evaporative emission vent control implausible signal


I cleared these and ran again for a while, P0021, P0431, and P0199 came back more or less right away. I have had a rough idle in the past, so I checked the various vent lines again + the air oil separator gasket - all look sound, and all have been replaced somewhat recently as well. However, because the codes are all coming from one bank, my thinking is more toward the cam on bank 2 now: maybe the camshaft position sensor is at fault or variable timing solenoid is a bit gummed up. I checked the angles and found bank 2 has a deviation of 3 degrees, not sure if that is significant enough to come into play. Raising the RPM and watching the angles in real time seemed to show the cams responding and adjusting evenly and in step with one another. Also not certain if the O2 sensors on that side are feeding poor information, but not getting any codes indicating that. 


Finally, the oil sensor is definitely gone, I have a new one ready to install on my next oil service, which is coming up pretty shortly. This behavior predates the sensor failure, but has been getting worse lately. Plugs are fairly new, coils I checked as well when I did the plugs. The general feeling of vibration I get from the warm engine I am chalking up to aging engine mounts, which have never been replaced to my knowledge. 


Any insight you might have to share on what may be the source of my codes would be greatly appreciated.  


Thanks, Mark

Edited by Papagut
adding a little detail regarding engine mounts, hoping the edit may also generate more activity
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  • 3 months later...

I'm going to chime in with my solution here just in case someone experiences a similar issue: I started with replacing coils and plugs in the cylinders that were misfiring as I wanted to rule that out. Simple solution really - almost all of the codes cleared up, starts and runs much more smoothly. I was not aware that warming up has an effect on coils/plugs - so I suppose I learned something there. 


Good luck if you run into the same issue.



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