I am getting the P0171 code "System too Lean", which is giving me terrible gas mileage. When I reset the code, it comes on minutes later, at idle, before I drive around.

I have stock maf, stock exhaust, stock cat, etc... My only mods are HKS 280/280 cams, Supertech springs/retainers, and Walbro 255 pump. Emery tuned my car on 93 octane, and it runs great.

Usually P0171 points towards a vacuum leak or bad o2 sensor, but I don't think that is the case here. My car idles great (right around 900 rpm), doesn't ever stall or flutter, and pulls safe afr on the dyno. I have checked for leaks, but maybe I missed something?

Anyways, could my large cams be throwing the code at idle because they are moving more air than expected at idle? Emery seems to think that this is a possible problem, but it is hard to test for, other than increasing my idle. Anyone else have this problem from large cams?

Also, if it is o2 related, is P0171 bank 1 system too lean the front or rear o2?

Thanks for the help!

-mark

 

It's probably a vaccum line on the back side of the intake manifold by the throttle body. It's very skinny and downlow and easy to miss.

 

It could be, but I think that the cams may be the case more-so than the vac leak, since I don't have any other symptoms than the code. No idle problems, etc..

If it was an o2 sensor, would it register seconds after starting the car, or does it wait until the car fully warms up?

-mark

 

Sorry I was thinking of a different code when I replied.

 

Bump!

Another reason I don't think it is the o2 sensor is that it happens while the car is warming up. If it were an o2 sensor, it wouldn't even throw the code until the car fully warms up, correct?

 

Replace the front O2 sensor and that should help. I think I had that when I my dynoflash tune destroyed mine because it ran so rich.