PICK SPEED LATER, CUTTING OUT

I AM HAVING A JETTA 4, 2001 MODEL 1.6 ENGENE, FUEL(PETROL), I HAVE A PROBLEM WHEN I CHANGE TO GEAR TWO, IT SEEMS LIKE IT PICK SPEED LATER, CUTTING OUT, I HAVE TRY TO CHANGE THE PLUGS BUT IT STILL DO THE SAME THINGS, PLEASE HELP ME

I HAVE CHANGE ENGINE SPEED SENSOR BUT IT STILL DO THE SAME THING, THE COMPUTER CANT DETECT ANYTHING SO FAR,