No power when cold, code PO171

ISING4U

MEMBER
1999 TOYOTA 4RUNNER
3.4L
6 CYL
4WD
AUTOMATIC
170,800 MILES

Live in north Georgia with insulated garage. When engine cold, cannot pull my 35 degree short driveway; engine must warm up. Seems like less power while climbing hills in our mountain home area. Yesterday check engine light came on with PO171 code, indicating possible Mass Air Flow Sensor issue. Don't think this ever changed. SUV has only ~ 2000 miles yearly of mostly mountain miles over past 15 years.

1 Reply

94 TRANSAM

MECHANIC
680 POSTS

Hello, welcome to 2CarPros. Let me see if I can give you a hand with this.
A Toyota PO171 is a generic code for bank 1 lean. There are several things it could be so I will give you the most common in order of cost to try to save you some money hoping it is a cheap fix.

The first is a dirty (MAF) Mass Air Flow Sensor

https://www.2carpros.com/articles/mass-air-flow-service

Second would be a leaking vacuum line or intake manifold. Visually check each line and listen for hissing, this will indicate a leak. If you find none then get a can of carburetor cleaner and carefully lightly spray all the way around the intake manifold with the engine running. If the motor speeds up at any point this indicates a leak and will require you replace the intake gasket. Please note! Carburetor clean is extremely flammable. Do not carelessly spray it everywhere. 1/2 second shots in each spot is all you need.

Third would be to replace the O2 sensor on bank 1. Here is a video on how to do that:

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

Let us know what you find, if this helped and if you got it fixed. If none of this works please come back and we can try some more.
Rich