1999 Ranger PO171 and PO174

Hello, I have a 1999 Ford Ranger 4.0L 4x2 with 91K miles. My Check Engine Light recently came on and gave the codes PO171 AND PO174. I checked my airfilter and it was infact dirty, I had forgotten to change it during the past two oil changes. I replaced with a new one and deleted codes but CE came back on several days later. I then removed the MASS and cleaned with sensorKLEEN but it was crystal clean to begin with. I also checked fuel pressure and Vacuum leaks, everything turned up perfect. There has been no change in the way the truck runs or the gas mileage. If I clear the codes out with my scantool the light will stay off until it's below 50 degrees outside then it turns back on during cold to warm up. Does anyone have any suggestions? I have read so many forums and I'm out of remedies...Would disconnecting my battery and allowing the ECM to reprogram possibly help? Is this different than deleting the codes with my scan tool? Thanks in advance for any suggestions!

Hello, I have a 1999 Ford Ranger 4.0L 4x2 with 91K miles. My Check Engine Light recently came on and gave the codes PO171 AND PO174.
In the Taurus thread, they just posted this as a sticky http://www.automotiveforums.com/vbulletin/showthread.php?t=768631 regarding the exact DTC codes for a 2000 Duratec. I would imagine the codes are similar.

Good luck!

I have the same model/year Ranger. Several months ago my CEL came on indicating the same codes which I believe had something to do with the PCM reading a lean mixture. Two possibilities came to mind. One is a malfunctioning O2 sensors or you may have a vacuum leam. Since the codes indicated a lean mixture in both banks, I ruled out the O2 sensors at this pooint on the premise that both O2 sensors, one in each bank, could'nt be bad at the same time - but possible. Instead I checked the vacuum system, hoses, power brake booster, and alike including the intake manifold. With the engine idling, I sprayed a throttle valve cleaner in suspected areas and watched any change in engine idle quality. Lo and behold, I found a leak in the right/forward section of the intake manifold. When I directed the spray in that area, my engine to momentarily hesitate. The mechanic wanted $428.00 to fix it as he insisted I needed a new intake manifold. I did the job for $15.00 by replacing the "O" ring gasket. The CEL went out by itself after three restarts. This may not be applicable to your case but it's an option to take.

if its a lean code then you should be checking for vacuum leaks of any kind. you could also check your O2 sensors.