Not sure if this has happened to anyone, but here is my story. Bought a 2004 XC90 2.5 AWD in October, car was inspected a mechanic and runs well, no problems. At the end of November it got colder and "check engine" light came on, the code was for random missfiring of cylinders 2 and 5. Light kept going on and off for couple of weeks, took to mechanic. Spark plugs did not look good and were replaced, but that was not the case; coils looked good, but they decided to put new coils in cylinders 2 and 5, but that did not fix it, so they placed old back (did not charge me for that). Head gasket was checked to be ok. As a last test they checked for pressure in each cylinder and found out that when it's COLD outside, cylinder 2 does not hold any compressions and all other cylinders are very low. When the car gets warm, all cylinders are functioning well and test shows good compressions. If the car stayed outside over night and it was below 40 degrees, check engine lights up, but while driving during the day, it goes away. Mechnic recommended valve job, which could be anywhere from $2,500 and $5,000 depending on what they find once they get in there; buteventhis mechanic agreed with me that it might not worth it to fix the car. They also saidthat it is very possible to drive another 100k miles with this and nothing might happen, but there is always a chance that it might not start one day. Spoke to a friend on the other side of a country who is Volvo Service manager, he has not seen a car with only 42k miles on it that needed a valve job. I was thinking of taking it to a dealership for a second opinion, but don't really see any reason, they will have to run the same test.
Has anyone exprienced anything similar? Or can there be something else wrong that mechnic missed? Thanks.

 

I would start with running a really good cleaner through the system something like Techron.

 

The EXACT same thing is happening to me with the exact same vehicle (04 XC90 2.5T),bought the car in Nov and in Dec it got really cold and same symptoms came up, same engine codes Cyl 2 & 5, intermittent misfire, wont start or hard to start when cold... took it to several places, changed the coils, the fuel rail, spark plugs, new battery etc.. the list goes on and still having the same problems on and off. We're scratching our heads trying to figure this problem out, it wont start when its below -20, changed nearly everything and thinking about maybe needing a new engine? And so, today I took it to a garage guy I know around here to have a compression leak down test done and it passed with nothing wrong? .. Then he took it for a test drive, came back and claimed it had a slight loss of power and hesitation. He then proceeded to lift the vehicle up to check the exhaust while the car was running. Said it sounded like the catalytic converter was plugged. Well turns out the exhaust needs replacing and the catalytic converter ran very hot. I will be changing the whole exhaust system this week and see if that fixes the problem. Would love to hear back from the original poster and see what his problem was. Anyways I'll keep you posted if anyone is having similar problems.