when my truck (22re) is around 1500 rpms or lower at idle it makes a putter sound once in awhile? it runs great and rev's great so not sure if its a problem or not? btw im getting a CEL for running lean mixture what could it be?

 

What's the maintanence history of the truck?
Oil, timing chain, valve adjustment, filters, sensors (esp o2), and more...

 

oil ever 3k miles, dont no anything about that other stuff except i always check my airfilter. i need to do a gas filter though soon