My daughter drove it to work last week and the CEL came on while driving home. I check the OBD and A2 = 4-4-3. Of course, this has never happened to me in the last year or so. I cleared it and when my daughter drove it again yesterday, same thing!

I have replaced all but one of the vacuum lines, the elbows look good. I find no air leaks around the intake manifold. Yes, the car is running slightly rich as the exhaust pipe is black.

I have no maintenance history. Who knows how old the O2 sensors are? Last thing I did was to replace the turbo Boost control and it's 4 vacuum lines. No leaks. The car runs like a bandit, starts easily, and is generally fun to drive. What I don't want to do is throw parts at it.

Here is what Volvo says to do:

Code 4-4-3 (TWC Efficiency) TWC = catalytic converter.
1) Check for other codes. If any code for misfiring is stored
(Codes 4-5-1, 4-5-2, 4-5-3, 4-5-4, 4-5-5, 5-4-2, 5-4-3, 5-5-1, 5-5-2,
5-5-3, 5-5-4, 5-5-5, 5-4-4 or 5-4-5) perform that testing first. If
Codes 4-3-5 or 4-3-6 are stored, perform testing for that code first.
If none of the above codes are stored, go to next step.
2) Perform a compression check on all cylinders. Repair as
necessary. If compression is okay, go to next step.
3) Check for air leakage in intake system. Repair as
necessary. If there is no air leakage in intake system, check for air
leakage in exhaust system. Repair as necessary. If there is no air
leakage in exhaust system, check fuel and residual pressure. Repair as
necessary. If fuel and residual pressure are okay, retest using new
TWC.
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Keeping it running is better than buying new