I've noticed the last few weeks when i'm on the bike i'll be holding the throttle still trying to hold a certain speed and noticed it isn't holding steady, like it's being moved slightly yet I have the throttle still.

Any ideas?

My first thought is the air filter needs cleaning, but i'm not sure.. could this be the cause?
I think it was serviced by the garage before i bought it, and that was about 4k miles ago, is it about time to clean it?

It's a DNA filter btw.