Want this question answered?
yes
In the gas tank. I have 2001 Echo.
2001 Toyota Echo doesn't have a timing belt.
http://www.carspace.com/guides/Toyota-Echo-How-to-change-oil
http://pdftown.com/2000-2002-Toyota-Echo-Service-Manual.html
It's electronic.
You may simply need to clean the MAF Sensor. Simple fix.
Sensors of this nature normally generate their own return signals based on speed and temperature under varying conditions, they are not constant values.
The one closest to the exhaust manifold is the upstream O2 sensor.
You can get a refurbished one for about $70. See: http://lmgtfy.com/?q=toyota+echo+mass+airflow+sensor
Its included in the following instructions for changing out the post cat O2 sensor. http://www.carspace.com/guides/Toyota-Echo-How-to-change-post-catalytic-O2-Sensor
3.5 Liters