Bad Fuel Injector - what causes this?

[ccorbridge]

Looks like I have a bad fuel injector. I think this can be caused by bad gas, but what other possible causes are there? Just wanting to understand in case there may be other related problems.

I just bought my 4runner and have no idea of it's history.

 

[RonMAIDEN]

Age can be a big factor and if no injector cleaner was ever ran through it can cause issues and cheap gas but it's liley age on the older 3rd gens.
My mom takes very good care of her '99 Limited and she had an injector go bad just this year with 90k on the truck;I have 163k miles on mine and my injectors still work fine.