I have a 92 535is manual and would grateful for any help on the below topics.

Firstly I have bought a pre cat exhaust as I want to do away with the cats, what happens with the lamda sensor when I fit this? Can I disconnect it?

Then I want to richen the fueling up, I have a power boost valve so should I play with that or is ok to adjust the air flow meter? I know it would be best to have the ECU all remapped on a rolling road but does anyone know anything about these cheap chips that are being sold on ebay, people rate them in the feed back?

And one last question (for now), my fan (blower) has started making a noise (where it ticks away as though there's a leaf stuck in there) is there an easy fix?

Many thanks in advance