Problems when idle and now power at low revs

I just started having this problem & im very confused. I noticed that when i was driving and taking off from 1st gear between 800rpm -> 2000 rpm there is no power, however after 2000rpm the car goes fine.
Along with this problem i noticed that when the car is idle at a set of lights the revs start fluctuating between 500rpm -> 1100rpm. Noticably this happened on a hot weekend.

BTW. in both occasions the engine temp gauge stays below the 1/2 way mark.

I only recently had it service and replaced the air filter. I was wondering if anyone has any ideas on what is wrong with my car.

Thanks in Advance

reset ur ecu and then start the car up and let it idle for like 5-10 minutes before driving to set everything back to standard. after driving for a little the ecu will adapt itself to changes and ur car will run better.