Jetta Trek '96 idling high

I have a 1996 Jetta Trek 2.0 litre 5-speed (206,000 km) that has been starting rough in the mornings (also noticeable smell of exhaust - also can smell exhuast when sitting at a traffic light) since the weather got colder (winter time in Canada). Today, after getting off the highway on my way to work the engine RPM's stayed around 3000 when I put in the clutch to downshift. It took a few minutes before I could get the car down to around 900 where it usually idles. This happened back in December as well but hasn't since then so I didn't worry about it again until now.

I've been reading this could be related to the mass air flow sensor (MAF) covered in oil/dirt. I replaced my air filter last year and it did have oil in it, but at the time thought that was related to another oil leak that was fixed due a faulty rocker arm. Now I'm not so sure. Any advice? Thanks.

Check for a clogged PCV valve. Probably either that or a vaccum leak.