What do you think are the pros and cons of removing the air pump. I am considering removing one on my 1990 L98.

There are no cons that i know of!!

removal of the air pump without removing the main cat will saturrate the cat from excess fueling on startup and ruin the cat in short order, lose emission compliance (visual, probably sniffer) and have you cleaning dirty things in a lot of areas that you can now see. That said, I removed mine (Hawaii) and have you dreaming of a turbo or supercharger to put in the new found space! Aloha

It's free spinning so no horsepower gain. I got rid of mine because it was making noise. Like case said, no cons as far as I could see. Unless you remove the whole thing, then maybe fail a visual test....but if you have high flow cats on, then you should pass regardless I would think.

If anything it'll help the cat if you remove the air pump. It sends air to the cat to help burn off hydrocarbons. During rich conditions the smog valve dumps the air into the engine compartment to prevent cooking the cat. I'd say combustion in the cat is worse for it than just passing gas fumes through it. Obviously your emissions on cold starts will be worse. Otherwise the sniffer won't know the difference unless your car is moderately out odf tune.