There is a rhythmic drumming noise coming from under the hood?

A day or so after I got it, I noticed a rhythmic drumming noise coming from under the hood. At least 80% of the time. Whether I was accelerating, idling, decelerating, it didn't matter. There was no rhyme or reason that would trigger it or make it stop that I could figure. If you picked up the air flow hose (which runs to the throttle body and the IACV) and put your hand over that hole, it muffled the noise. The guy I bought it from said the idle air sensor needed to be replaced when I asked him what it was.

To be honest, I know nothing about cars, and it didn't affect the way it drove. So, I drove it like that for about 2 months. I know. You don't even have to say it.

Anyway, today it decided to break up the monotony and try some new stuff; like accelerating all by itself and constantly idling at excessive RPMs. I'm 99% sure the drumming noise is completely and totally gone. And even after reading the manual, I don't know how to get the instrument panel to show me the RPMs or if it's even possible, so I don't know exactly how high it's idling. I can tell you that if you don't hold onto your drink and brace yourself, you're likely to spill it or even end up on the floorboard yourself at the mighty lurch it gives when shifting into drive. The jerk is noticeably smaller when shifting into reverse though. I thought maybe longer to shift into drive = more time for the engine to rev= bigger jerk. So, I tried reverse after letting it run for a few. Still wasn't nearly as bad as drive.
While driving home after this started, I hit 60 MPH on the highway without stepping on the gas. Going up sharp inclines or even gradual ones for any length of time was the only thing that plateaued and even slightly decreased (by 2-4 mph) my steadily increasing mph. Mostly, I had to ride the brake or slow way down and then let it climb, slow down, climb, etc.
I took the IACV off, cleaned it, and put it back on. No difference. My friend tried to unplug the valve. No difference. But he unplugged it while the car was running, which I've read would just make it stay in the last position?
So, my questions are, would the IACV cause that drumming? Is there possibly a vacuum leak? Or would that only cause low idle? And could it be the throttle position sensor or the other throttle sensor? And how do I figure it out? Thanks in advance for any answers. Please just remember, I know nothing about cars, so very in-depth descriptions and explanations (think cars for dummies), even pictures would be so appreciated. Thanks again!

Bad IACV? Or vacuum issue? Or both?