1993 940 I get a whistling noise from the engine compartment but only when the weather turns cold. Gets louder as you accelerate.

When the weather turns warm it disapears.

are you getting the noise when the engine warms up?
i'm getting the same thing but after the engine warms up, the sound disappears.
haven't had time to poke around yet to see what's going on or what's making the noise.
if you've found anything, it'd sure help me out as well :)

With a plastic hose you can make a stethoscope and pinpoint the source. Also, with a digital camera you can make a movie and post it on photobucket. Then we can hear it! Might help.

Could be a timing belt tensioner bearing, alternator bearing something along those lines was my first thought.

When you accelerate how do you hear under the hood?

If it is actually coming from under the dash. It maybe a vacumm leak from a door motor or the brake booster.

If the sound fills the car when the windows are down, it may be your drive shaft support bearing below and right behind your seat.

Bearings are subject to temperature changes and with load shifts.

Try to squeeze the idle valve intake hose and see if the noise changes.

Thanks I'll check