15 Jetta engine is unstable at idle speed when the temperature is about 40 degrees. What is the reason?

Reasons for unstable idle speed of cold car engine: 1, poor oil circuit leads to unstable idle speed of cold car engine. Usually, the nozzle of the EFI vehicle is blocked or the control circuit is faulty. Need to clean the nozzle. If it is a circuit fault, the control circuit needs to be repaired or replaced. 2. Too much carbon deposit in the engine causes the valve and intake pipe to be blocked, which makes the engine idling unstable. It can be solved by cleaning the intake valve and intake pipe. 3. The spark plug is damaged, or the engine is unstable at cold idle due to excessive carbon deposition. Spark plugs need to be cleaned or replaced. 4, ignition circuit fault caused by low voltage or voltage instability makes the engine cold idle instability. The ignition circuit needs to be replaced to solve the problem.