holy crap.. I've been thru these two questions a few times before..
You mean the AFM (Air Flow Meter), yes you can put a filter but you need an AFM adapter bracket to put a filter on it. I'll post pics later on as I'm not at home.
For your jumping idle, do this. Find the idle screw, then raise the rpm until it doesn't jump up and down anymore (probably about 2000rpm) then leave it there for a minute or two. Then slowly start to lower it until it hits about 900-1000rpm. Hopefully this should get rid of your jumping idle. I've done it a few times already and it works.