i have a 99 ford ranger 4.0. the codes po171 and po174 keep coming up on my check engine light. these codes read the mixture is too LEAN. i have looked for vac leaks and clean my MAS sensor. i have also replaced my o2 sensors and checked my PCV valve. i was wondering if these codes could be coming up due the the throttle poisiton sensor being bad. does anybody know how i could check this? i can tell my truck is not running right. it seems to skip before going into overdrive and the other morning i went outside to start it to warm it up since it was cold and when i came back out my truck stopped running. does anyone have any solutions? thanks.

 

I see where you checked your PCV valve. Did you go ahead and change it?

 

no, i just took it off and cleaned it out with carb cleaner.

 

Had the same issue with my "new" 98 I bought in July. The CEL was on with these codes and an O2 sensor when I bought it. Changed all 3 O2's because of the mileage and all the codes went away. As it's cooled down here in Missouri, about once a week I would get a 0174 code. Last week we had some 35 degree mornings and all 3 days got 0171 and 0174 codes. I suspected an intake gasket and decided to change them. (Had to on another 98 I had for other reasons). The truck also has 130K on it and wanted to clean the injectors and intake anyway. I bought Felpro gaskets and liked the lower gasket, it has built in collars so you can't over/under tighten it. The uppers are just formed o-rings, and mine were flat and broke when I removed them. It also came with another EGR O'ring for where the EGR tube feeds the intake. Anyway after an afternoon of cleaning everything untill I can eat off of it, I've not had either of the codes since on some chilly mornings. It also solved a random 1st start of the day rough/erratic idle I was having that some people have also talked about.

Also, if you do this, don't forget new O-rings for your injectors, and retorque your lower intake bolts while your there. This is my 4th Ranger (if you count my 93 Exploder) and so far the first 3 have gone 250K and were running good when I sold them. I hope to get this out of my "new" 98.
CJ

 

Welcome to FTE.

The 4.0L is known for intake manafold gasket leaks, so seeing as how you have lean codes for both cylinder banks, seems to me the intake should be on your suspect list.

Maybe rig a propane "sniffer" with some small dia tubing & a sports needle on the end as a probe & see if you can get a rpm rise out of the engine while probing the intake gasket area.

Let us know what you find.

 

I agree with suspecting the intake manifold gaskets, especially since I'm guessing that this came up just as the weather got cold, right?

I posted this about this time last year and there are links to other P0171/P0174 threads in the first post:
Cold Weather Related Issues Informational Thread

-Jim

 

no. the cold weather is not just the issue. it has gone on for a few months. but here lately i think it is starting to get worse.