I ended up opening up the console yesterday, while it was 15 degrees outside. It is hard to be careful and work on the console while the car is running. But it is also nice and warm that way...

Anyway, I was pulling and tugging on different vacuum lines and the whole hissing noise stopped. Now I can't re-create it, and I don't have a clue what was making it to begin with. So, chalk up another victory to the self-repairing Volvo. I'm sure it's repair job will fail at some miserable moment, but you can't trace a problem that isn't happening.

As an aside, the car is still running like crp, only when it is at idle, then I step on the gas and let it back to idle. Maybe a TB problem or an idle switch problem. Just gives me something to do this weekend, if it isn' too cold.

Some guys have all the luck! There are some small vaccuum hoses in there, also a horizontal vaccuum accumulator. Looks like a series of plastic balls. I guess that a series of spheres is less prone to collapse than a simple tank! But why should the system hold vaccuum at all if you have the kind of leak that makes the motor run funny?

If you take the hard plastic side panels off you may be able to figure out what is going on.

Good luck...I was in there last weekend-changed out the blower motor, and my hands look like I tried to drag a wild cat through a barbed-wire fence.

Chris,

There's a quart-sized plastic bottle mounted just behind the firewall to the left of the passenger's footwell. Holds a vacuum from the intake manifold through a small black hose on my 86 240.

Mine has always made hissing or wooshing sounds under the conditions you describe, but I don't have any drivebility problems. I always thought this was normal.