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.

Could be a number of things causing this. Start with the easy/cheap things first, and cleaning the air filter would be a good starting point.

Also check for vacuum leaks in the throttle body, fast idle mechanism and the inlet rubber (between throttle body and head) which is prone to perishing. Any unmetered air entering the engine will cause erratic engine speed.

__________________

I have the same thing. My old xt600 1992 did the same.

Its not 100% smooth and you can feel it. It happens random but often when you hold throttle at same position.