Volkswagen golf 1999 Throttle stops working in cold and damp conditions

ignition wires and coils are very common replacement items on these vehicles, damp and wet weather are sure signs of misfires, stalls and no start conditions, have your local technician test for coil/wire arcing when wet.

make sure your rad. cooling fans work does this only happen at slow speeds or when stopped?

I'm not familiar with the Renault specifically, but most vehicles have a method of dealing with carburetor icing. When the weather is cool and damp and the air is sucked into either a carburetor or throttle body, the air pressure changes.
Inside the intake manifold there is a significant vacuum condition. That sudden drop in air pressure causes the air temperature to drop significantly and can cause humidity in the air to condense on any available surface. While the rest of the engine is quite hot, the air intake can be quite cold.
After running for a period of time, an ice ball can develop on the inside of the air intake; when that occurs, the engine will be incapable of proper operation and can stop running, at which point the heat from the engine will diffuse, warming the intake and melting the ice.
To solve that problem, most vehicle manufacturers use a carburetor de-icing system that basically consists of a tube that runs from around the exhaust manifold up to the air intake. By the time any ice can start to build up on the inside of the air intake, the outside of the exhaust manifold has become quite warm, and any air that passes the exhaust manifold is heated enough to prevent the icing problem.
So the short answer is, make certain that the tube is in place, provided that Renault's used that system.

"I have a 1996 Golf III GSX. I had the timing belt
Problem with the 2001 Volkswagen Golf" Can you confirm whether your car is 1996 or 2001, I am assuming from GSX it is a 2.0 inj? If 1996 I would say quite simply an air leak on the inlet side (likely to be the inlet manifold gasket or a small pipe that has come disconnected) If 2001 try a throttle body reset, it could be a calibration fault. Come back to me with more details / questions if you wish Regards Lloyd

sounds as if your mass air meter is badthis will cause the fluctuation in rpm it is located on the airfilter box

sounds like the thermostat stickng as when engine gets cold the choke will start workin again, causing the over reving or your electric fan is on all the time "over cooling" the engine

check the owners manual to make sure youre using the right oil. cars do lose compression when theyre cold, thats why it is so important to warm up the car before driving in cold weather.

Have you checked the spark plug wires?
They tend to cause this when conditions are right (or wrong), especially when heated up or cold and damp. If your mechanic checked it only when warm, not hot they might have overlooked the matter.

If your car is fuel injection,try changing the cold start temp sender.

try to clean the throttle body with some carb cleaner, if that does not work, then you are looking at either the idle control valve, or worse the whole throttle body,