I know over care about my car & nag too much on this forum... but on occasions my RPM & when on neutral sticks on 1500... I don't know why but when this happens i notice that my engine sounds quieter & feels struggling in someway...

Sounds like the idle valve is sticking....

Could be the idle valve, it has a small internal gasket that can fail, I took the top off mine, threw the gasket away and used instant gasket on it - works a treat now!

Also check the throttle cable, sounds basic but if its getting snagged somewhere it could cause the issue.

Or the "spring" the cable is attached to, but that's probably what LRB had in mind!