Thats happened to me more than once . A piece of dirt somewheres I guess

Yup, sounds like there may have been a sticky shaft on the TB, or a little crud stuck in the IAC. It happens. When's the last time the TB was off the truck? Doesn't hurt to pull it and clean the crud that builds up on the back of the butterflies. While you're at it, clean the IAC ports, as well as the IAC itself. Just don't immerse the IAC motor in any solvents. Not good for 'em, and really not good for the wallet if you have to go get a new one.

Now, whatever you do, DO NOT run it long with no air-box/filter/inlet. If you do, you put your engine at grave risk. There is a LOT of air being pulled into that plenum, and ANYTHING that's loose under the hood is liable to get pulled right on in there. Bugs, dirt, small pebbles, etc, will NOT be good for your intake valves. If you're just thrashing one and TRYING to blow it up, that's a good way to start. The air box has two purposes. 1, as stated, it's a snorkel to pull cool air in over the header panel, and holds the air filter. 2. Ever notice the fresh air comes in from the bottom? It's also a water separater. Water into running engine equals BAD, unless you're running a water injection system for performance. But I don't think I've seen that trick since the early 70's.