Have a 2001 S40 with about 73K miles, I searched but could not find anything with these codes. I am having a rough idle when sitting at stop lights and the car is in drive. The rpms will drop, the car stutters for a moment and then it is ok.

Had 7 codes and replaced the MAF and MAP and now down to 3:

P139
P171
P172


The book says that with codes P171 and P172 together it could be MAF but I already replaced that. It goes on to say O2 sensor or vacum leak.


Just wanted to get some feedback before I replaced anything else.

 

Check good for Vaccum leaks.
Maybe a Bad o2 sensor.

But Fuel pressure could also have an affect on that code.

Look in the front of the intake there is a Bigger hose that comes out they are known to break.

 

I will check those, thanks. The other thing I noticed was that if it is in park and I rev it, the car will rev then rpms go low an the car dies.

 

Check them things first that will cause this to happen.