I have a 98 passat 1.8t, with an automatic transmission, and i want to change it for a 2002 passat 1.8t engine also with automatice transmission, but i want to change just the engine, or the block off the engine. so i have a ? if there is a difference and what i would have to change or modify. thanks.

The engine is basically the same. You will need the ecm and new engine harness. you will also need a different throttle body (electrical not throttle cable style.) May need a new transmission harness. Different cooling system so the coolant lines will be different (98 external water pump 02 timing belt driven w-pump)