It's crumbling away on the bottom and leaking some kind of fluid.
Today after I changed my oil and was driving home the truck started to stumble and was wanting to die. Of course I was freaked out cuz I thought I had screwed something up during the change. After I shut it off it took a long extended crank to get it start again. For the most part it still runs and drives fine, except now it idles slightly higher (1000 now vs 750 before) and if I quickly blip the throttle from idle it'll stumble and almost die before picking itself back up. If I ease onto the throttle it revs like normal. Sometimes when I would get deep on the throttle while driving the same kind of stumbling would occur. Could the leaky thing in the picture be the culprit? There's a vacuum line coming off it going to somewhere on the intake so I figured it's a good place to start. I'll admit I'm kind of embarrassed I have no idea what it is haha. Thanks for your input!