Seat Marbella

Hello, I have a Seat Marbella 900 of the year 96, when I go out in first or second, the temperature pilot is turned on and the car gives bright brines, I get clutch and leave and it is removed, on the highway on a fifth when it passes 100 kmth, it returns to do the same, but it does not stop jumping, I have to release the accelerator it seems that the car is going to disassemble the continuous jumps. That, thank you very much, greetings.