Varying the Engine Speed

Can someone tell me how I can very the engine speed from the engine bay? Not as apparently, easy as when there was a throttle bar.
A few weeks ago I started getting a strange sound from the drive end of the engine (I made a post about it at the time - "New Noise for me and my LS" - 9/29/17 ). Initially, it was only when the A/C was on and accelerating from idle which lasted only several seconds. But now it is starting to produce the sound when the A/C is off. It's necessary to vary the engine speed for me to find what is causing this crazy sound.

Thanks.