Kickdown switch

The transmission warning light came on in my 316i automatic when I pressed down on the kickdown switch below the accelerator pedal so I changed the switch (even I could do it!) but the problem remains. After pressing the switch the car surges forward and then comes back like taking the foot off the pedal but tachometer rev is above 3000 (2000 before) and the warning light comes on. This doesn't happen when I put the shift to 3,2 or 1 position but in these positions the car accelerates but after about 3500 rev the car jerks as if there is fuel shortage. I don't know if these problems are linked. Any ideas before I take the car to the BMW guys who are adept at emptying your pockets!