idling issues

Ok, so I just changed my oil, and as I was returning to my parking space, I did a few quick revs...and the idle dropped down to 500 or lower...wtf? It idles normally at lights and stuff at 700-800, but when I reved it like that it went low and borderline to stalling...it recovered, but still. Also the exhuast was poping a bit...I assumed it was just backpressure and nothing to worry about...anyway, any ideas...I'm not fooling with the idle screw, that's not it...perhaps spark plugs?

I have had that EXACT problem multiple times. My dad said it sounds like something wrong with the exhaust, but it is just not enough pressure coming through. I haven't had the problem in a while though. I never figured it out though, let me know what you discover.