I had to send ED-E home t pick up another companion, and now.. he doesn't appear to be anywhere, The game told me he was headed back to the Lucky 38, but he's not there or at Primm.. anyone know where he could be hiding?

I had the same issue. He appeared in Freeside (on his way to the 38) several real life hours (a couple of ingame weeks) after I sent him there (when I had already given up and forgotten about him). God knows why the trip took so long, but he did get there eventually.

He has to float there all on his own. How long have you waited?

If you are unable to find your companion despite waiting or fast traveling, go to Vault 22 and take the elevator to the second floor (oxygen recycling). Your companion will be directly in front of you when you step out. It even works when the companion has been told to "Wait here." This can only be done if you have a repair skill of 50 or if you have completed the quest in that vault.

Taken from fallout.wikia.com

ED-E turned up after a couple game days, apparently floating is slower than walking.. I suppose Veronica's power armor helped too.

I'm having the same problem with ED-E, Scrubwolfe, thanks for the help, but the problem with that solution is that the follower must be lost, when their following you, since I and Rilauven, have sent ED-E back to the lucky 38, he wont show up at the bottom of that elevator. Rilauven, I would recommend you continue waiting (In-Game) and check in the Lucky thirty-eight in about 10 in game days or so? hopefully that helps?!

Bottom of the elevator? They always show up in the Presidential Suite for me.