What is wrong with my car? The 'S' light is on?

My 91 Honda Accord has the 'S' light on and it is in a constant rev between 3 and 4, I drive the car in D4 gear, if I drive it like a stick and start in gear 1 the rev will go down when i switch to gear 2 but not when i switch to gear 3 or 4

The "S" light is a setting button on the side of the gear shift that brings the gears through at a compression faster than it would normally. The overrevving between 3 and 4 means you should have the transmission looked at, but it's not the sports (S) button.