r/VolvoS40

I have a 2011 Volvo S40 T5 throwing codes ECM-850D, 9200, 921D, and 922D. I recently replaced the throttle body and drove about 100 miles with no issues, but today the codes came back and the car went into reduced engine performance/limp mode.
While it was in limp mode, I was stopped with my foot on the brake and noticed the RPMs were fluctuating between 1000–2000 on their own. I shut the car off, restarted it, and it drove normally again for about 15 miles with no issues.
Has anyone experienced this or have any ideas what could be causing it? Wiring, ECM, or throttle adaptation issue?
See comments for codes.

I'm purchasing a 2008 S40 this week. $4400, 133K miles. Used car dealership. Had a PPI done onsite with Pomcar. Got an excellent rating. Was curious if anyone has any thoughts/comments/words of wisdom (or caution lol). I really love the car. Have been looking for a while. They are extremely hard to find...

Recent service history:

100K miles:

Camshaft seal(s) replaced

Drive belt tensioner pulley replaced

Drive belt tensioner replaced

Serpentine belt replaced

Serpentine tensioner replaced

Timing belt replaced

Timing belt tensioner/idler replaced

120K:

Ball joint(s) replaced

Control arm(s) replaced

Four wheel alignment performed

Power steering checked

Rack and pinion replaced

Steering/suspension checked

127K:

Front brake pads replaced

Front brake rotor(s) replaced

Rear brake pads replaced

Rear brake rotor(s) replaced

Coolant reservoir replaced