Okay so I have 95 940 Turbo that has a pretty small exhaust leak somewhere around the turbo/manifold area. It has 197k miles and was a one owner. On a cold start the car won't idle high for a few seconds like it did before, it revs a little high and then just settles back down to normal rpm...and you can hear the exhaust leak a lot clearer. When it warms up it goes away completely but I still feel the rpms fluctuate slightly when i'm in boost. How do I find out exactly where the crack is and how do I fix it? I also smell carbon monoxide or gas fumes on startup for a few seconds until the engine warms. Is this common for these cars or is odd?

Gas mileage is also terrible

 

A common problem that causes that is one or more exhaust manifold studs crack/break - there are 2 studs for each cylinder and 4 gaskets - carefully inspect each - look for a piece of an exhaust manifold gasket coming out from the edge near a stud - there will probably be a broken stud there. If you are feeling brave use a wrench or socket on each of the 8 nuts to make sure they are tight - be prepared when the nut fall loose to have to remove the manifold/turbo and drill the broken studs out of the head - it's not an easy job accurately drilling a broken steel stud out of an aluminum head freehand - especially the studs near the rear of the engine - you may need a right angle drill to get to the rear ones. If you get it wrong the manifold will not go back on the head - then you have to remove the head and send it to a machine shop. If that's above your pay grade be prepared to pay many hours labor - all sorts of stuff is going to break on a 25 year old 200k mile turbo car when trying to remove and replace the turbo/exhaust manifold.

For poor gas mileage check all of the hoses to and from the intercooler - they tend to get holes in them - check the short one on the drivers side - they burn through at the bottom.

 

I'd soak those nuts/studs liberally with good penetrant oil if you attempt to loosen or tighten them, they do break easily, also do with with hot engine as they come easier just like with the spark plugs.

If one of those four gaskets is bad and leaking, the whole manifold has to be loosened to change any or all of them. Fortunately the head removal is not that hard on this car. Whenever I have had broken studs I take the head to a machine shop and for $20 they fix the broken stud. From experience, one, even two broken studs don't necessarily cause leaking problems as long as they are not next to each other... that car with 200k probably can use a head gasket soon anyway.