I replaced my sons alternator on his 2005 S40 AWD 6 speed 2.5 turbo, Getting 14.3 to 14.7 volts when running from multimeter. However it has real running problem now. Starts but then dies at times, very rough idle at times. But then sometimes it will idle absolutely fine. I let it idle for 10 minutes then check engine light came on. P2178 and P1001. MAF issue. I did not have to remove the MAF. However the throttle control valve wires and alternator wire was moved around a great deal. At one point the car actually drove very well for 5 minutes until I turned it off but then had a very hard time getting it to idle again. The alternator wire is a 3 pin but has only 1 wire coming out of it. I’m pretty much at a lost.



just unplugged MAF, car run great with it unplugged.
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I'd start by cleaning the MAF, and if that didn't work, I'd replace it. It's not that expensive, and the symptoms sure point in that direction.

Also, there should be more than one wire running to the alternator - the heavy one that runs more or less directly to the battery, and the sense wire that connects to the alternator's voltage regulator input. Without that connection, I'm not sure how the alternator will act - it's always possible that the alternator is freaking out and supplying too much (or too little?) voltage at any given time.

 

I bought a new MAF, nothing changed. From reading on the net people are saying that the 2005 Volvo’s are very particular on what alternator they like. I bought the new one from auto Zone. Gives proper volts but the computer is not reading the info it is receiving because of the way the auto zone alternator is sending the info. Basically the computer and the alternator are not communicating at all levels, most but not all. Auto Zone will take everything back and they still have my old alternator so I can get the numbers. I am not absolutely sure that’s the issue, planning on trying to pick some brains at either Volvo or local foreign repair shop before I pay double for a Volvo alternator. Has anyone else had similar issue? My sons loves the car but this is ridiculous!

 

I have had issues with reman alternators on my 2005. Sometimes the car likes it. Sometimes the car hates it. See if you have a rebuilder locally that can rebuild the OEM unit with quality parts.

 

Thanks for your input. I took it to a local garage that specializes in Volvo, Mercedes, and BMWs for some advice. They suggested that I return the alternator and purchase a Bosch, they gave me a part # from using my vin. I planned on having them do a diagnostic but they actually suggested that it may not do any good because certain cars can be very particular. They actually spent a lot of time with me, nice to experience that kind of consideration. So I ordered the alternator. Should be interesting to see what it does.