Idle Problem

[sp33dy69]

Im having a bit of problem with the ideling, when i come off the motorway it seems to stay at 1,500rmp and then slowly (VERY SLOW) drops to 1000 but before it use to stay at around 800-900 regardless of where i was driving. it also does this in and around town but not so bad its about 1,200 then slowly drops. ive just cleaned the tb as my car kept stalling so used some of the advice from others and cleaned the tb. now all of a sudden it idels funny!! any ideas of what it could be?? thanx