2004 fx4 190k miles. 5.4
The dreaded 171-174 codes. Truck has air raid intake ,Gibson exhaust ..PCM was played with years ago.last week ford reprogrammed to stock"..maf ,o2 s ,brake booster , all changed..cat s replaced 2 years ago..cel on all the time.
Fuel trims ,LT maxed at 30 ,ST18-20 ..runs perfect won't pass inspection. DMV will not register. NY ..smoke tested no vacuum leaks..I clear codes and kam within 30 minutes same thing. Help winter is coming ..

 

If you still have the stock intake, put it back on.

 

Thanks good thought didn't work.

 

You have major air entering the intake somewhere after the MAF or you aren't getting enough fuel. I'd take a good look at the FPDM and change the fuel filter.