The Patient: 2000 Volvo S40, early model (04/04/2000), 146k miles, 1.9 Turbo
I started feeling misfires and hesitation and was waiting for the CEL to come on but it didn't so tonight I decided to read codes anyway. The result was...interesting... to say the least:

17 error codes, 9 of which pending

P0101 Mass Air Flow (MAF) Circuit Range/Performance Problem
P0130 02 Sensor Circuit Malfunction (Bank I Sensor 1)
P0300 Random/Multiple Cylinder Misfire Detected
P0650 Malfunction Indicator Lamp (MIL) Control Circuit Malfunction
P0234 Engine Overboost Condition
P0351 Ignition Coil A Primary/Secondary Circuit Malfunction
P0352 Ignition Coil B Primary/Secondary Circuit Malfunction
P0013 Exhaust Cam Position Actuator Open Circuit - Bank 1
plus all of the above as pending codes and also
P0172 P System too Rich (Bank 1) - Pending

Luckily I had ordered new coils and wires a few days ago and they came today. I had them installed right before I read the codes. That should take care of P0351 and P0352.

For everything else I would be happy about any advice. As usual I'd love to get by without dumping a bucket of money on the problem(s) but if I have to...

PS: After I read the codes I realized that I had never seen the CEL, not even when I first turn on the ignition and every control light is on for a few seconds. I'll have to look in the manual to find out where in the dash it is even supposed to be.

 

Update:
I had replaced coils and wires just before I figured out that there are 17 codes. I took the car to work the next day and used O'Reilly's Code reader to get some freeze frame data. Then I cleared all codes and read them out again. The P0650 (MIL malfunctioning) came back immediately, as expected.
I drove about 50 miles home after that and so far no codes have returned.
I'll keep updating

 

Update 2:
After driving another 50 miles I now have another code back, P0130. I might have to replace the O2 sensor.