01 toyota avalon with codes PO300-306 car runs rough and idles rough now while driving it start loosing power and making a snake rattling sound

SOURCE: Rattle/Vibration from front of vehicle when idling at stop

Hi and welcome to FixYa. Please try this:
GO out to the car, and lift up on the hood. Does it raise a bit and rattle? If so;
Open the hood, and look at the perimeter of the front radiator support. You will see 2 small rubber thingys, that look like that they are screwed onto the metal that is holding the radiator. Unscrew them a little, and close the hood. Pull up on the hood and see if the rattle goes away. If not, repeat unscrewing the rubber things until the lift disappears.

A FixYa rating (4 blue diamonds) would be greatly appreciated for my assistance.

SOURCE: Idle and gear shifting 1987 celica automatic

I would suggest hat you replace the timing belt. The noise that you hear is the belt.

SOURCE: idle too low on hot starts 2001 Avalon

Sounds like you idle air control valve is going bad. They start acting up on a hot engine due to sticking or high resistance through its internal windings. It will get to the point where the engine will stall every time you take your foot off the gas.
I suggest getting it replaced and the throttle body cleaned at the same time since it will need to be removed to replace the IAC.

SOURCE: 1999 Toyota Camry V6 idles rough and stalls after

yes it could be a fuel related problem, when was your last tune up, it could also be a spark issue, old or corroted spark plugs will sometimes not put out the correct amount of heat to ignite the gas correctly till it runs for a while, if the check engine light isnt lit, it will almost have to be something simular to this