Starting from the top. I have a 2002 5.4 supercrew 4x4. 147k miles on it. since the day I bought it new, I like a few others, have had that coil problem that pops up now and then. A couple of times the dealer had to replace a coil or two. Well no problems for a few years. About 6 months ago the service engine soon light came on, thinking it was a coil or bad gas I continued to drive local short trips for about 2 or 3 days and the bad idle went away and the light disappeared. It just happened recently and this time it started with a steady light that progressed to a flashing light. I knew this was not good, I parked it in my drive and smelled bad exhaust fumes. I figured a cat or cats got fried by one or more of bad coils. I figured it was time to replace the coils, plugs, cats, o2 sensors, I cleaned mass air sensor, I found one pvc valve and replaced it, cleaned intake and egr valve of carbon they looked good anyway. So I just completed the work. Now truck runs great on the short couple of trips I have taken. The service engine soon light came back on. The auto part store scanned it and it came back a p1131 code. I have no idea what that points to other than a possible vacuum problem somewhere. Oh it might be noted I see on the print out the auto parts store gave me, the code definition says: lack of ho2s-11 switch, sensor indicates lean. How would you guys recommend I proceed. Thanks

 

Did you replace the cats??

 

Check all your O2 senser plugs, make sure the connections are tight, free of corrosion and have diaelectric grass in them. Let us know

 

Yep I replaced the cats. I will be checking the passenger side o2 sensor today, heck I will take a look at everything again. So I should put a little diaelectric grease on the o2 connectors? I was not sure about that. Can do though.

 

Make sure the connectors aren't green or have a coating on them, get some electrical contact cleaner, spray it in there dry it out real good and put dielectric grease in there, sometimes when there is corrosion they read like that happened to me, quick easy thing to do befor looking any farther

 

Took wheel off and other stuff. Looked at passenger side o2 sensor. The sensor was disconnected, I thought I had connected it but perhaps it did not "click". Well light is off for now so perhaps that did the trick. Now I know what code the passenger top sensor will throw. Thanks for the input gentlemen.

 

UPDATE:
Today check engine light came on. Truck runs great, no hesitation or bad idle. Autozone guy says codes p0171 and p0174.
To me everything looks fine, I sprayed mass airflow sensor clean, going to see if code comes back on later after I connect battery. So hell if I know. Thought about changing out dpfe because I hear those have a high fail rate, but I thought the truck would idle ruff if that fails.