Timing running rich or lean
 

Car keeps throwing codes - running rich as oil gets older so I threw in some higher viscosity oil, now it throws the P0012 retarded code. Anyone figure out how to fix this error code without having to change the oil all the time?? Swapped out both VVT and Cam sensor - still have error.

73K miles on a 2009 T6 XC70

the VVT is driven by oil pressure and the galleys can get clogged over time so throwing in thicker oil will probably make the problem worse. My suggestion is to go back to correct weight oil and use a brand name full synthetic. I suppose you can try a Seafoam treatment to see if that removes any gunk. When you say you swapped out the VVT what exactly did you do? If you pulled off the gear, have you checked the timing marks? With that said, I'm not sure how the running rich condition correlates to the oil's age. How did you determine the engine is running rich? ie are you getting CEL codes or misfires or sooty plugs?

Mt6127 I changed the timing valves, intake and exhaust, and cam position sensor. As the oil ages you get a running rich bank1 PO172 code. Of course as the oil ages it gets thinner, so I added a quart of thicker than suggested oil but still within Volvo specs, to the proper levels of course. It went from a P0172 to a P0012

Intake (A) Camshaft Position Timing – Over-Retarded (Bank 1)

I swapped out the new parts and replaced them with the original parts, same error.
If I change the oil and replace the filter, the car runs fine for a few weeks then back to the P0172 error. It seems like a common problem with these cars and all anyone says is "change the oil". I am looking for an actual solution.

OK so I had the oil changed - 25miles on a new oil change and it threw the P0012 code again. I am at a loss...

I'm wondering if you need to check the timing marks on the cam gear - you say you replaced the solenoid and sensor so the only other component in play is the cam gear. usually when cam gears fail they create oil leaks which you didn't mention so I'd have to think its either timed wrong or you may have connectivity issues. perhaps cleaning the connectors and reseating the ECU? Ever test for system voltage while driving to see if it drops below 12V or so periodically (can cause spurious fault codes)? It may be worth the $150 to have a Volvo shop do some run time diagnostics for you.

UPDATE: Try, Try Again...
 

Bought the replacement DIAPHRAGM and put it in, code cleared and didn't appear again for 700 miles. This means I actually got 1400 miles of running on the last oil change before the code came back. The replacement part spring was taller and bit stiffer than the one I removed. The part change and clearing code allowed me to pass inspection as the check engine light was off. Replacing the part was cheaper than the oil change! This 2009 vehicle only has 74K on it, used by a little old lady, really.

No major oil leaks, it could be the battery. I will run the scanner on it while going for a ride and see what comes up on the voltage.