Thread: o2 Sensor, P0171, Surging Idle

Car has code P0171 (Bank 1 Too Lean) watching on my scanner the o2 voltage stays at .05 at idle. The exhaust smells VERY rich. So I figured my o2 was bad. Replaced it with a new Denso one and same exact thing. If I rev the car up a bit the o2 starts oscillating properly. The car is modded and has been tuned. Below I have my thought of what could be causing this.


-Bad Tune (When I bought the car I had a code for bank 1 too rich caused by a bad FPR. If the car was tuned with the bad pressure regulator and now it's been fixed it would be getting too much fuel....???)

-XPZ Cam Has too much overlap and is allowing raw fuel and air to enter the exhaust at idle

-Headers have the o2 bung back too far? (Seems unlikely but just a thought)

Not really an easy solution to any of the things I've thought of so far so hopefully somebody else has better ideas......preferably something that cost me under 5 dollars and is a guaranteed fix.

Thanks guys

Originally Posted by Scottydoggs

maf could need to be cleaned. vac leak. or th eo2 is bad. id check for vac leaks, then if you dont find any clean the maf.

I already check for vacuum leaks before replacing the FPR and found none. The o2 is new and I cleaned the MAF when I got the car and did a bunch of other preventive maintenance. Looking at the MAF data while the car is running the output looks ok and goes up and down pretty smoothly with the RPM although I dont exactly know what to look for. Its a northstar MAF as well

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