2002 V40 146,500 miles: Car is garaged every night in heated apartment garage, which maintains temperature around 40 degrees Fahrenheit in winter.

Morning start-up without touching the gas pedal, initially the RPM's move above 1000, then the engine begins to stall with RPM's moving to around 500 and a throaty sound like a hole in the exhaust manifold can be heard and then it corrects itself and idle returns above 1000's and it hunts in that range for a minute before settling down at 750. If I do not let the car warm up for a few minutes, it will stall when put into gear, however it will not stall if I let it run on it's own with touching anything. Throaty/exhaust sound goes away, for the day after start-up.

I also get an exhaust smell when accelerating, not strong but noticeable, I have had the car inspected at a Midas muffler but they could find no leaks, and I am sure they wanted to find one.

Lastly, engine is dry accept for around the upper black hose hose connecting to the turbo, I assume this is the inter-cooler, not wet but tell-tale oily residue.

After replacing thermostat and temperature sensor, codes read:
P0172 -System Too Rich Bank 1
P0101 - Mass air-flow sensor
P0015- Variable valve timing
P0139 -O2 sensor Bank1/S2

Spark plugs have been changed, with performance NGK Iridium, and look good on inspection, if a little rich.
I sprayed the Air Mass with CRC cleaner.
Change oil every 3-5k miles at Valvoline Auto Center.
New air filter with last oil change

I am looking for any guidance on which repair I should tackle first as I have been told, that the issues could be related and correcting one problem may solve multiple codes.I would rather not purchase new air-mass unit, O2 Sensors and VVT unit needlessly, nor do all the work if unnecessary. I perform most work myself, unless a lift is required.

Any suggestions are greatly appreciated, and as always thanks in advance. This is a great forum.

Red Floyd
'02 V40

 

Not likely to be the O2 sensor. That code is saying the sensor can't compensate for an upstream problem. A few things to research - 1) the idle air control valve and 2) fuel pressure regulator. The IAC lets air in during idle and can impact cold start ups. The fuel pressure if not proper (ie bleeds down over night) can appear as a MAF issue. Unfortunately the FPR is not cheap so you may want to inspect/clean the IAC first. Browse the S40 board as there's some good posts on this topic.