Hi! First post! So on NYE I was on the highway in my 1993 240, it was -5 degrees and I was driving 70 mph. I had been on the road for about 40 minutes when the gas pedal became stuck down. Like when I let off the gas, it would keep going like cruise control.

I managed to exit the highway and get the car turned off (it was scary!). I turned it back on again briefly hoping it would have reset itself or something, but it immediately revved up like I had the pedal to the floor.

I had to get towed home. The tow truck driver said he thought the throttle was frozen open - like the cable froze to the housing or something.

 

I had that problem on a Geo Metro. Didn't make enough heat to heat the throttle body and if I didn't let it warm up a little 5-10 min in really cold Minnesota weather there were times the throttle would stick. It's still something you need to check out by pulling the duct off off the throttle body to see if you can see frost on the throttle plate or sides that would jam the plate. With the bitter weather it's likely but could also be some slush getting on the outside of the TB or like you mentioned moisture inside the cable too.
If you can try to get some lube pushed into the cable and maybe spray the linkage on the outside of the TB's throttle linkage with oil (not WD40, oil).

 

The 1st logical thing to do is open the hood and turn the throttle cable by hand to the home (closed) position. Start the engine and see if it runs at normal idle. Spray some WD40 around the throttle body and the linkage. Check the cable to make sure it is not binding. Spray the cable too. Waiting a week for the weather to warm up isn't the solution. If it still runs fast then have it towed to a garage to get it fixed.

 

I'm not sure if this applies to you or not, but my 940 has a preheat hose that routes warm air from the exhaust manifold, into the airbox under cold conditions. This is controlled by a thermostat on the airbox inlet.

You should check to see if your 240 has this feature, and if it does, make sure its working properly. The system is designed to prevent this exact issue from happening.

 

I did wait until the temperature raised, turned it and saw that it moved freely and wasn't frozen anymore. Greased the cable. It's running fine now! Thanks for your help!