I have to clean the whole air intake system every 6 months or less because it's clogged with oil residues that are spitted from the flame trap that's right on top on the throttle valve, the valve itself has to be carefully cleaned every time the idle goes bad, it runs very well after I clean the whole thing, including the flame trap and hoses.
Why would Volvo put this oil vapors exit on top of the air intake with no foam filter at all like many other cars have, could I just buy a piece of foam for another car's air filter and put it inside the flame trap capsule? there could be some restriction but I would keep the air intake system much cleaner.
I am using synthetic oil now and it's better than regular oil, it was much worse before but it's still a problem.