My passat accelerates only to idle

Hello friends, I have a passat 1.9 TDI of 2001 and my problem is as follows: the car accelerates only to idle when I start, it climbs to 1100rpm for about 5 seconds and then returns to the normal idle and does so 2 or 3 times. During the march the car is going well I have not noticed anything, the only thing that I do not know if it will have to do is that the water temperature needle has its own life and goes up and down when you want, if someone can help me locate the fault I will be very grateful to 2.