Hi, I have a mercury sable 2000 it has 256k miles on it but it’s still running. I’ve had moderate maintenance on it late april this year, getting a new EGR valve, spark plugs and new seals replaced, and fixed piping etc. and after driving it about 170 miles, two new problems sprang up. the first is that there’s this hissing/airy noise that I can hear from the passengers side but only when i press the accelerator. it doesnt make the sound when im idle or rev up in park/neutral. secondly, there’s smoke thats coming from the serpentine belt. its white and its not a lot but its visible if you’re looking. I cant tell if its a rubber smell, but the smell goes away after 5 minutes or so. I took it to my usual backyard mechanic(not the same guy that worked on my car in april), but he says he just thinks there’s oil residue on parts of the engine that’s burning it off, as he noticed i had my seals replaced recently because there was oil getting into my spark plugs. but im going to get a second opinion
for a bit more information about the car, i got the hydro pump replaced 2 years ago and a tensioner pulley replaced 1 year ago. I do not drive the car a lot except for the 170 mile trips back home and that’s once every… 8 months or so, most of the time im local. The oil and radiator fluid are still at normal levels and i don’t see any leak spots on the ground. My car does have a rough idle and it does lose power at idle unless i run it for some time then it idles normally. even though the hissing and the smoking occurs, there’s no noticeable difference in the driving than it was before I fixed it. theres no other weird noises i hear besides what i described above. My engine light is on but its for the oxygen sensor I have to fix soon.