idles and reves fine in park, but in drive it dies while sitting still

Also possibly loose / cracked or damaged sit inlet tube from air cleaner assembly to intake plenum .. May need *hands-on* guidance (?)

The big rubber *air tube* can be easily damaged during air filter replacement.

you got that right! what a poor design for Toyota. if you're not careful when lifting the top of the air box (lid),that plastic fitting with the rubber hose attached to it will snap off that comes out of the side of it and hooks to a little metal pipe. I just went to the scrap yard and bought a used air box for mine(someone broke it and tried to glue it back before I got the car, but that failed! before the guy at the scrap yard tried to pull that hose off the little metal tube,I stopped him and told him to cut the metal tube and I would cut the hose off when I got it home,put a new hose on it,a little grease,easy to remove and put back now.the air intake hose is Dorman Part Number 696-717 and they are proud of that hose,although there are some non branded ones on ebay for less than $15.00 or so....

The Air Filter hasn't been replaced since I bought the vehicle last October, and have only put 5000 miles on since bought, so I don't think that's the problem. I just went out and ran it... it does fine until the engine warms up, and then that's when the problem starts. After the engine warmed up, I sat there and watched the RPM's go from 800 , drop suddenly to 200, then rebound immediately back to 800, holds RPM's just fine for a few seconds then RPM's drop fast again and rise just as fast. It will do that RPM dropping/rising a few times, then the next time it starts to do it, the car dies.