Difference between Slow down and Slow up

slow down—

1. move or work at a slower rate:

• If the driver wishes to slow down he does not necessarily change his gear, but operates the accelerator.

2. live in a quieter less active manner:

• New York is a place where you can’t slow down…. Any person tends to vegetate unless he is moving on a fast track.

slow up—

1. = slow down 1:

• The bus slowed up to allow the passengers to get on board.

2. = slow down 2:

• The doctor advised Jim to slow up for a time, to give his heart a chance.