well two actually!

what is the air pump for in the engine bay? is this an emmisions thing?

also

on my dashboard near the windscreen is a sensor. what is this for?

thank you

 

air pump warms up the cat upon cold start up to extend its life

 

So in theory, without the cat in I could loose it?

 

thats a temp sensor by the windshield

 

air pump (as mentioned) is to help warm the cat. If you loose the cat, you can loose the air pump. Make sure to block it off, if it's removed.
Zoom nailed the sensor.

If you have any more dumb questions, post in the following thread, instead of starting a new one
https://www.rx8club.com/rx-8-discuss...llowed-208221/