FIXED ! - Codes P0171 and P0174, Occasional rough idle.

[ehnco]

It turns out that in my case it was a lower intake manifold vacuum leak. (Although the propane enrichment test and spraying ether failed to locate the leak). I have the OHV, and they were all very loose....seemed to be less than hand tight actually. I retorqued them to spec. (3 steps, according to my Haynes manual). Final torque spec. is 144 inch lbs. Reset ECM and have driven 8 drives cycles so far with no CEL and no occasional rough idle as before. After verifying that this was the problem, I changed the plugs and fuel filter. It had a FRAM filter installed. Took it off and compared flow through new and old. THe FRAM appeared to be very restrictive compared to the Motorcraft replacement. No more FRAM products on my vehicles. Has anyone retorqued their intake and had to replace the gaskets anyway ?? I am hoping this is not a short term fix.......not something I want to do anytime soon. 108,000 miles and otherwise trouble free...so far...

 

[TheRookie]

I am doing the retorque tomorrow if all goes well. Changing out my injectors at the same time. I hope I am as lucky as you

 

[Billy177]

the gaskets should be fine if they were gonna blow out then they would have when the manifold was loose

 

[ehnco]

Cool. So far, still no CEL. Knock on wood......