P0171 2002 Toyota Corolla -

Question

I have replaced both oxygen sensors before and after the cat converter. I replaced the air cleaner but the check engine light still comes on and gives me a 171 error code. Don't know what else to do.

Answer 1

P0171 Fuel trim lean Bank 1

Lean condition are mostly cause by vacuum leaks, whether it comes from the EGR valve leaking to a EGR gasket. use brake cleaner spray around the suspected area, if there is a noticable drop with the RPM you found it

 Check also the sparkplug making sure they are properly torque down and not loose

 And just for a quick check with the engine at normal operating temperature feel the radiator hose for any over pressure situation. a coolant seepage into the cylinder will set a lean code condition which can be investigated by doing a leak down test.