Carman850.

I had a similar problem with the throtle cable on my W124 300CE-24 after I had the engine bay steam cleaned. It would rev up when it shouldn't, the only way to bring it back down was to stick it in neutral and pump the accelerator. When I got home, I removed the air filter unit, which gave me access to the throttle linkages. I then used a degreasant and cleaned them up again. Then I put some clean grease on them, out of an aerosol can. This will keep it clean and to some extent protect it from the cold. Not sure if it will protect down to -26ºC

Haven't had any trouble since and that was 2 years ago.

Hope this helps.