Vibration at idle, especially with automatic transmission, is usually caused by engine idling to slow. Now, since there is no idle adjustment screw anymore you need to have the vehicle checked at your Toyota Dealer. Some vibration, even to that level is normal. IF IT HAPPENS IN THE PROCESS OF STOPPING, WHILE BRAKING, YOUR BRAKE ROTORS ARE LIKELY OUT OF ROUND.
get a wheel alignment
a/c kicks on
motor mounts
If it's just occasionally, it may be a sticky thermostat.
Bad tire or alignment is most common. It can also be caused by a warped brake rotor or drum.
Alignment
Worn steering parts, worn suspension parts, tires out of balance, out of alignment,
One of the main causes of feeling a vibration in the gas pedal is engine vibration. The vibration from the engine causes the accelerator cable or linkage to vibrate and the vibration can be felt in the gas pedal. Check with a mechanic to be sure.
The 2004 Toyota Tacoma does have a built-in anti-siphoning device in the gas tank pipe. This device erased the need for locking gas caps, but causes a problem when the gas tank needs to be emptied to make repairs.
It is important to know the causes of bad car performance. In a Toyota Avalon, the symptoms of a bad steering rack are as follows, slips in steering, the car pulling to one side, and the steering wheel bounces up and down while driving.
Trouble code P0420 means: Catalyst System Efficiency Below Threshold (Bank 1)
it cause it to vibrate!