Hello all. Looking for some insight and/or starting points. Have a 97 Accord DX, automatic, with 223K miles. Upon startup, the engine revs high as most Hondas do, around 2000 rpms. Engine runs fine. After about 20-30 seconds, upon driving, the car misfires. Press the gas, nothing, almost like it's about to backfire. I floor it, and after a mile or so, it stops and runs fine. Only happens upon startup cold. Starting doing it sporadically, but has gotten worse and recently threw P0171 "system too lean". Reset it and it came back 20 miles later. I also gave it a complete tuneup recently including fuel filter, plugs, wires, pcv valve, cap, rotor, all with genuine Honda parts. Any help would be appreciated. Thanks!!

 

Although P0171 can be caused by many things, such as air leaks, it can also be caused by the primary O2 sensor on your car.

 

My sons 97 LX did exactly the same thing, bogged badly when trying to accelerate and threw a P0171. Upstream O2 sensor fixed it right up! Curiously, it never gave me a code to tell me the O2 sensor was bad....

P0171 can also be caused by low fuel pressure, intake vacuum leak, sticky PVC valve, EGR valve not seating properly or an exhaust leak upstream of the O2 sensor.

I tested fuel pressure and it was fine. I sprayed brake cleaner all over the intake manifold and rubber hoses and idle speed did not change at all, thus, no intake leak. I think if you had an exhaust leak up stream of the O2 sensor, you'd hear it. My PCV valve was brand new. You can check yours by removing it and giving it a shake. You should be able to hear the plunger rattling inside. If not, you can try cleaning it with carb cleaner, Amsoil Power Foam etc., or just replace it, (its pretty dang cheap at Auto Zone).

Since you just replaced the fuel filter, that means for fuel pressure to be low, your fuel pump or fuel pressure regulator would be bad.

Odds are, it's the upstream O2 sensor....

Best Regards,
Michael Rush

 

Thanks Michaelrush01, I just bought a fuel pressure tester. Once I figure that out, the consensus seems to think the primary O2 sensor may be shot. Thanks for your input.