When i slow down by cat to about 5-10kms or close to stop, and mash down the clutch pedal, my rpm shoots up to about 1000-1500rpm.

What can be the cause of that?

also the idle dosent stay still. it idles sometimes at 900rpm or sometimes 800rpm.
depends. also moves a little from 800 +/- 100rpm sometimes. dont know if this is related.