A couple of weeks ago my 1999 Expedition 5.4 EB with 157K miles threw codes p0171 & p0174...lean on both banks. Like many others, I found that the PCV hose was leaking. I replaced the hose, reset the SEL, & everything was fine.
Then...a few days later I get code P0401...insufficient EGR air flow. So despite the fact that many here said don't waste time replacing the EGR valve, I decide to do it anyway...& both bolts holding the EGR onto the throttle body break off.
Well, I always wanted to clean the throttle body & now I have the opportunity. So I remove the entire throttle body & take it to a shop so they can drill the bolts out which they did. I also had them clean the throttle body. I got it back in one day & it looked brand new. I get the truck put back together & there is a very obvious noticable improvement in throttle response. The truck starts & runs like new. Then...the next day I get the P0401 code again. I sprayed the MAF sensor with electronic cleaner as well as all of the connectors. Last year I replaced the DPFE sensor.
What do I do next? My truck runs great but I want to get rid of this code.
Thanks in advance for everyones help!

John

 

EGR sensor is all that's left to the EGR system if the valve is new.

On a side note, some electronic contact cleaners leave a waxy residue to prevent corrosion. The residue also stops the sensor from reading correctly.

 

Make sure the small tubes that are going to the DPFE sensor and hoses are clear of debris. As well as the EGR tube. There is a small orifice in there. Next, try to clean out or replace the DPFE sensor again, expecially if it was an aftermarket sensor. If it just throws the code with no difference in performance it's probably a bad DPFE sensor.

 

I took the DPFE sensor off tonight but there really isn't much you can do with it. Can I spray electronics cleaner in the tubes?
Thanks,
John

 

Theres a post around about someone that actually took it apart and cleaned it out. I don't see any problem with spraying electronic cleaner in the tubes. But I would check the EGR tube first and spray as a last resort. I don't think it will hurt the sensor but I wouldn't use any type of brake or throttle body cleaner.

 

I had the code for insufficient EGR flow on my 98 Expedition with 5.4L engine. I replaced the EGR valve, and the DPFE sensor (new Ford model) and still had the problem. It turned out that the problem was caused by damaged vacuum lines right next to the battery. I had 3 lines that were aged, abraded or chewed by critters. I patched the vacuum lines, and the problem disappeared. That was about 6 months ago. Some of the members on this forum helped me find the problem...thanks, guys. Thanks also for the information about the leaking PCV hose. I now have trouble codes for left and right banks lean. I'll check the PCV hose.