My 400 dollar 850 has been serving me well over the last year or so, runs like a bear. It's been throwing P0171 and p0455 codes for a while, but I've been just erasing them with my code reader.
Last week I was coming home and she stalled. Wouldn't run unless I shut the key all the way off and restarted, and then only for about 10-20 seconds. Fortunately I was close to home and limped her in.
I figured it might be some bad gas (tank was low) so I put in some fuel treatment and eventually got it running again. Took it for a spin around the block but the next morning same problem--shut key all the way off and she'll run for 30 seconds.
Changed out the fuel pump relay, no difference. Jumped 87 to 15 and she will run but a little rough.
Today I did a new fuel pump and filter and she started right up, but after 10 minutes of idling it started to run rough and bog when I hit the gas.
I'm going for the MAF sensor next, however when I unplug it when it's running it makes no difference, when I plug the MAF back in it runs smooth for 2 seconds and then back to rough.
Any ideas?

 

the codes are telling you the car is running lean and the evap system has an issue. You may have an air leak, particularly on the vacuum line back to the cannister (a smoke test would help with this if its not easy to find). Another cause of the 171 can be the MAF, particularly if the intake looks dirty or oily. A quick fix would be to get some CRC MAF cleaner and do the MAF, idle air valve and throttle body to see if that helps. Next thing would be to measure fuel pressure to see if the pump is able to keep up.