My Tiptronic doesn't like the hot weather

[Dale_K]

I drove the car 30 miles yesterday in hot weather with the vacuum source line coming from the manifold plugged with a golf tee. When I got home there was a genuine hissing (not a vacuum leak) from the Tip while in reverse only (it's been doing this for a while in the heat) but no hissing otherwise and no stumbling at idle the way it did before when the vacuum leak was active.

There's no telling how long this valve has been broken in the closed position. I'm planning on replacing the valve rather than a bypass but every American car I'm familar with has a auto trans cooler mounted in the radiator that tends to bring the trans fluid temp to the engine coolant temp. In fact I'd think there would be some benifit from warming the trans fluid in cold weather.

I still don't know about the hissing in reverse but I'm planning on doing a Tip service by dropping the pan and replacing the filter. This will partially replace the fluid too.