Maybe I'm paranoid but...
 

when I open up my hood while idling, I can hear this subtle hissing noise, pretty high-pitched. I didn't notice it at first but once I caught it, I hear it all the time now.

A few days ago, I attempted to clean my throttle body. I was gonna take everything out but the screws on the ram-air thing didn't wanna come out, so I just opened up the big tube that goes from the air-box assembly to the TB; stuck the straw of my TB cleaner right in there and sprayed it while I had my friend rev it up to 2000rpm or so. I took the MAF sensor off because I thought someone on this forum said to so the engine wouldn't go higher than 2200rpm.

So, did I mess up something there that now makes the hissing noise? Did I introduce air leak where the tube attaches to? I made sure many times that the tube is on the TB correctly and the worm-gear tight. Or am I just paranoid and there's nothing wrong with the car? I think I notice some engine being a little hesitant but then maybe my mind is making that up...

Re: Maybe I'm paranoid but...
 

I think your just alittle paranoid. Whenever I clean my throttle body (same way you did it) My car gets a little hesitant for a bit cause you gotta wait until all the fluid is out. Then shes fine. :)

But is the hissing noise normal? Oh, and by the way, cleaning out the TB didn't do what I wanted: stopping engine from dying when coming to a stop with the gear in neutral - 2k, 5spd

Im not sure what kind of hissing noise your hearing, but if it wasn't doing it before, its definitely something you wanna check with a local mechanic or dealer.

You might wanna check this out
Clicky

And read section *Some additional Info about Throttle Body Cleaning*

Cool, thanks a lot for your help.

No problem :)