I read posts where codes 171 and 174 were left and right bank lean. Since both are pegging, whould you lean more towards a vacuum leak, or dirty maf sensor, as opposed to assuming that both oxygen sensors are bad? My 98 expo has 98k miles. Wouldn't it be a good idea to replace the O2 sensors anyway?

Thanks

 

in my case it was the rubber fuel pump hose had ruptured inside the tank.
hook up an efi fuel pressure gauge to the shrader valve on the pass. fuel rail.
wrap the line with a towel , run it up to the cowl and only shut the hood so that the safety latch catches. then drive it. if it idles below 30-32 psi and under heavy load is below 36+psi it's fuel delivery.
cheaper than throwing O2 sensors at it prematurely.

 

P0171 and P0174 codes simultaneously are normally due to a leak in the intake/vacuum system.

The PCV hose elbow seems to be the most common source.

Steve

 

Steve is right!

Replace pcv valve with hose: elbow near the wall cracked.


Marcos