P0171 Reading - Could really use some advice please!
 

Hello everyone.
I have a 1996 850 non turbo with a CEL on, reading P0171 running lean. My problems started about a week ago. The car had been driving fine when one day I started it up and it was having a rough idle, almost as though it was going to stall. I drove it about 3 miles to see if it would go away or if there were any other symptoms. When accelerating from a compete stop it would be the worst - almost stalling. After getting up speed it would be fine. The next day I started it up and it was running totally normal. I thought maybe it was a one time thing (clearly I am a car amateur but willing to learn!).

A few days later the thermostat started to act up. *I do not know if this is connected to my primary problem of rough idling and stalling with the P0171 reading* I checked coolant levels and radiator fan - both seemed fine. However I then noticed that even if my car had been sitting off for 10 hours, when I went to start it the thermostat would go all the way up to the middle as if the engine was warmed up (when in reality was cold). It would go up towards the red and then back down to the middle while driving and seemed to be more of a sensor thing than the car actually overheating. Again this might be a totally different problem but wanted to mention it since it did start about the same time.

Today is when the CEL came on and it got so bad that the car actually stalled. Before we had no idea what was wrong but with the light we were able to get the reading. They told us 3 possible causes:
1. Faulty heated 02 sensor
2. Large vacuum leak
3. Faulty MAF sensor.

I would REALLY appreciate it if anyone could give me some advice. Is there any way to test the three causes so I can figure out what the actual cause is before buying parts? Knowing the symptoms, does that make one of the causes more likely? Really ANY advice or experience would help me out alot. I love my Volvo and want to fix this as soon as possible. Also, should I keep driving it? It is the car I use to commute to work but I am worried about causing further damage.

Any help would be appreciated. Thank you so much for reading.
Katie

Thanks for the links! I did the PCV test and the glove did blow up. I am watching videos and doing research but will have to wait for my friend to look at it since that is a job beyond my expertise. Not sure where to begin.