02 Kia Sportage 2.0 dohc p0171

Need to get some other ideas on maybe a weird vacuum leak on this Sportage. I am getting a lean exhuast indication at idle. Off idle, switching fine. Setting a p0171. Fuel pressure 35psi, vacuum 18''. Changed upstream o2, fuel filter,pcv valve, cleaned throttle plate, cleaned injectors. Threw in a new set of plugs while I was there. Problem surfaced after extended storage caused dead battery. After recharging battery, vehicle misfired enough to set #4 misfire code. Cleared up misfire and now stuck with this. Misfire has not recured. Tried propane enrichment today and noticed no change in o2 voltages. Just looking for somebody else to bounce this one off of.
The first thing you have to establish is the engine running lean or is it that the computer thinks it is?

What happens too O2 reading(s) when you artificially (restrict air intake) create a rich mixture?
Can you force O2 front or rear to show rich at idle?
If you can, keep looking for reasons that’ll cause an engine too physically run lean.

O2 heater circuit; is there power to the circuit and what is the resistance value of the heater elements; 6 ohms @ 68 degree. If the heater is not functioning, the O2 maybe cooling off at idle and going off line?
If so, the computer might be seeing O2 flat line at approximately .5 of a volt or less, (ref. voltage). Adaptive fuel trim will now be pined rich adding fuel but the computer still sees lean and sets the code.

Check O2 readings with a voltmeter; then compare with scan tool’s readings. This will confirm that the computer is interpreting the signal properly.

One other thought; even though the down steam O2 is designed for catalyst efficiency monitoring; I’ve seen them affect fuel control, if defective and latched lean.

 

Thanks for the input Dan. After running myself in circles, the problem was found with a faster scanner than the one I was using. Customizing data to only show short term trim, a pinhole leak at the number 4 intake runner gasket was found with carb cleaner. The sensitivity of the program in the ECU is really the thing that confused me! Besides seeing the trim change in response to hitting the leak with the carb cleaner, the was no other sign of the leak. I'm getting too old to chase this stuff!