Location of spark plugs on a 2000 Toyota Echo

Sounds like an engine misfire.Does the check engine light come on or flash. If so, it may be a spark plug or ignition coil issue. The transmission can also cause a shudder problem. These transmissions are usually rather dependable though.

Take it to a dealer and let them check it out by plugging it in then checking the mapping of the computer ,i suspect a fault with the ECU but its difficult to tell without the right software .remember this mapping will be encoded to stop people like me reading the faults

Spark plugs are replaced when the electrodes are found to be corroded, burnt, cracked or oil fouled.
Normal spark plugs need to be replaced every subsequent 30,000 Km.
Iridium - tip spark plugs are replaced every 80,000 Km.

most of them are under the dash on passenger side of car i scrapped a 2002 echo and that's where it was located

You may have to get a shop to check it out.
You could have a problem with one of the injectors or the compression on one or more cylinders.
You also have a coil for each plug and the coil may not be firing the plug.

front of engine drivers side

It's in the gas tank. Found this on another site so all credit to the original poster. Anyways, here's the link that has very detailed instructions on how to replace it.
http://wiki.answers.com/Q/How_do_you_replace_the_fuel_filter_located_on_a_2000_Toyota_Echo

a fuel filter can be a cause of power drainage, but it can also be many other things, start by replacing the fuel filter, and if its not that then work your way to your spark plugs and plug wires so on so on.. making sure you change your oil, oil filter, air filter, fuel filter, ignition rotor, plugs, and plug wires is a great idea to tune up and restore some power back

Sounds like a fuel problem. Check fuel pump and fuel rail. Do a fuel line pressure test. Try cleaning inside of throttle body really good and also the TPS at that location. There's many things that can make a car run bad. 

most likely what is called a coil pack or - - spark plugs - there are several different ones - so be sure of ur model -- -
take the vin # down and call the dealer - - ask them their advice - also - ask them -- if there are any recalls or service bulletins