Why does my CVT over rev when cold?

I have a 340CVT which over-revs when cold. After the noisy first 3/4 mile it starts to work normally. That is it wants to do 3500rpm when cold at a throttle setting which would give 2200 when warm, accelerating through the 20-30mph region.

I fitted the noisy Roflex belts 3 years ago.
I put on a new 4-way valve then as well.

Do CVTs "go sticky"?
Do 4-way valves stick when cold?

Any ideas?

could it be that with the choke out you decrease the pressure inside the carb, to which the autobox's vacuum thingy is attached?

AAh

I should have said: I have also tried warming the engine up completely before driving off (not something you should do regularly) and it is exactly the same. This isn't an engine problem.

It also happens more in winter and less in summer - hence the temperature angle on my question...

What I will do is to pull the tube off the 4-way valve on a cold morning and check that there is vacuum with revs > 1800.

Well I pulled off the change-up vacuum tube and indeed there was more vacuum when the beast had been 2 miles.
I dismantled and WD40d the 4-way vacuum valve. Now it does not over-rev when taxiing up to the dual carriageway on estate roads.

But when I go off with any more than a very light throttle it goes up to 3300 much quicker when cold than when warm. I can only think this is due to stiffness in the transmission because the rubber belts are cold. They are much more flexible when hot.

The conclusions, then
1. The 4-way valve was sticking.
2. The transmission works better when hot
3. 5lab was right in that a cold engine makes less vacuum and thus more revs.

[foggyjames]

Will Plumber is the CVT expert around these parts, but no-one has heard from him in almost a year. Very odd! Try posting on www.volvo300mania.com, as there's a guy from the Netherlands who is very knowledgable on such matters.

cheers

James