I noticed the last few days my Ole 1985 240DL wagon has been idling a bit rough..But running good..Today when i was out and about out, out of the blue comes this sharp rapping noise at low rpm and under load..So i back off and the noise goes away..The engine sounds great as it always has...I push back on the peddle and the rapping noise is back..I also smell some raw exhaust and at the next light it is missing ever so slightly...So I'm thinking it almost sounds like the timing is way advanced and the sound is pre-ignition...Like it's trying to fire way to soon...Does this sound like a familiar Old Volvo problem that someones knows about??...Oil is clean and looking good...Just tuned it up a few months ago...This old car normally just purrs...Not a foul sound comes from it unless it's cold then you can hear a tiny bit of piston rattle until it warms up..Then it's pretty much gone...I am hoping this new problem rings a bell for some of you guys that know these Old 85 240s really well..What do you think???....Just a bit of History about the car..It has 250,000 miles on it..Doesn't use but a tiny bit of oil between changes..Timing belt is about a year old...Need your wisdom..:)..Thanks!!