Yesterday my V10 van developed these 2 codes and has a very bad idle:

P0171 - Bank 1 system too lean
P0174 - Bank 2 system too lean

Though some experimentation I took off the latter part of the intake/air filter assembly(start of air into the engine) with the mass air flow sensor detached and the van ran great. I plugged the whole assembly back in and it died. I tried to replace the MAF and that has not helped. A buddy of mine thinks that with the MAF not plugged in the FORD system is duping itself with some kind of MAF range that helps it to run well with out it and when it is plugged in, some other possible vacuum leak is causing the issue.

Please any ideas out there???

 

98% of the time, it's just a severe vacuum leak. Check the PVC hose assembly, especially the rubber elbows.

 

WHERE ARE THESE STUPID ELBOWS YOU GUYS ARE TALKING ABOUT xD?? cause I don't know one house from another on this truck so I'm at a loss for what to look for.

 

Make sure MAF sensor assembly has a "tight fit" into the air intake hose . it may leak if it is handled rough - and if it does, you will have unmetered air going into the system which may cause the same error codes you mentioned ) .

You need to erase the codes after each "fixing attempt " to see if they are coming back.

Good luck,

 

Well last night after getting the engine cover off I noticed that the master cylinder line was not clipped to anything else even though there was a hose clip on it. I clipped it up like it should have been and then followed it and made sure the rest of the line was ok. I then started the truck up and it runs great now. I am going to replace the master cylinder line soon, but am just glad the truck is running great now.