At what stage of modification should or must you remove the air pump?

 

When you eliminate emissions controls. If you still have your ACV and main cat, keep the airpump. If you have removed either of them, then the airpump is useless. If you are on the stock ECU and the airpump is disabled or removed, then you will probably have problems with stalling when the A/C is on. A car that can pass a smog exam will also be easier to sell and not leave that oily residue on your bumper.

 

The only time you HAVE to remove it would be when going to a single turbo setup that doesn't allow the air pump (most don't).