97- F150 5.4 Ltr check engine light has been on for 3 weeks. Engine cranks up and runs good. When heats up , at idle it goes from 1k rpm to 800 and then drops below 500. Friends advised O2 sensor was bad. Took truck to Auto Zone and they found the 2 codes on the computer. No recommendation as to what caused the problem, but the codes mean lean fuel mixture on bank 1 & 2. I changed the four O2 sensors and did not correct the problem. A local shop checked the truck out for 2 hours and could not determine the problem. Any suggestions.

 

check the pcv hose very close. where it goes to the back of the intake. you have a vac. leak. or another sensor giving pcm bad input. do you run a k&n filter. those things wipe out mass air flow sensor's like crazy. i would start with looking for a vac. leak. check all hoses the throttle body. also does truck run good while driveing. like fuel press. is ok. bummer on the o2's. those are costly. good luck.

 

Try changing the fuel filter if you have never changed it. The regular interval is 15K on these trucks.
Jes

 

Thanks for the responses.

Last night 08/26 around 10:30 PM after crusing this website I remembered I had to feed the horses. Armed with a flash light I walked past the truck. Rembering what other people had said about idling rough, I decided to look at the engine one more time. The PVC valve was on my mind this time. It was still pluggged into the valve cover. Checking further, I ran my hand around the back of the manifold and THERE IT WAS. The rubber elbow had rotted from the heat allowing the manifold to suck air. I would say a pretty crappy material used to make the elbow. It had almost completely dissolved away in the bend. Would you believe it, the local Ford Dearleship had sold their last hose assembly this morning. Thanks to Auto Zone and a friend of mine that works on I-55N, we engineered a hose for less than $6.00.
PROBLEM SOLVED

 

I had this happen to my '98 about 3 months ago. I just happened to find it because I heard it sucking air when I opened the hood up. The truck would actually die after awhile.
Ford charged me, I think it was, $27 for the whole hose assembly.
I couldn't believe that you can't get just the elbow. It is made of some pretty thin and crappy rubber. I too had to rig up a make shift hose for about a week before I got to a Ford dealership.
Now I have to change my plugs and that's going to be a big pain because of the location of the CoilOnPlugs.
Happy Fording Guys and Gals.

 

Good heads up guys!! Where is this elbow? Is it halfway between the PCV and the back of the TB? Or is the hose at the back of the TB "elbow" something else?? Nothing wrong with the truck, just want to avoid it if possible,,,,98