When to change sparks plugs into my echo 2000

a repair manual will probably tell you. it has maintenance schedules, models of commonly replaced parts (spark plugs, oil type, weight etc)

http://www.papertownspdf.com/downloads/toyota-yaris-echo-repair-manual-1999-2010/

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.

run the fault codes to find the problem . Guessing and changing items just costs money and becomes frustrating. With the engine light on it could be more serious than plugs and coil

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

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.

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

Try replacing the spark plug wires if you did not change them when you did the plugs. It is very important that you pull one and only one spark plug wire at a time to keep them in the correct order or your car will misfire. You should change your fuel filter every 30k miles and they are usually about $20. Try the wires first and see what happens.

Spark plugs do not need calibration!! Although it may need gapping which requires a gapping tool such as a filler guage!! Check your local autozone for this tool and gapping specs for this vehicle!!

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

ignition wire or oil leak at cylinder valve cover to spark plug