My girlfriend had the same code on her Toyota Echo. Thankfully, the car was still under warranty, and the dealership replaced the MAF. You might want to check the voltage of the MAF to see if it is working properly.rooster said:i ran the obdll checker on my friends palm pilot to find out why my cel light is on and the idle is rough,,,it said error o171 system too lean? how do i fix it? what could it be?