I have started noticing an issue with my truck when sitting and idling. It will drop from 900RPM to about 500RPM and just start running rough enough that the truck shakes from it. Additionally my Check Engine light came on and indicated these errors:

Bank 1 running too lean
Bank 2 running too lean
Bank 2 Sensor 1 Slow response

I just recently cleaned my MAF about 4 months ago so don't believe that to be the issue. Any ideas on what may be the case in this situation? I was thinking maybe a vacuum leak.


1998 F150 XLT 5.4L V8

 

With both banks lean its most likely a vacuum leak. More commonly known on the pcv valve side. Follow the pcv valve from the passenger cam cover, the line runs to the back of the throttle body/intake. There is an elbow back there that was known to fail, dry crack. Check for any collapsing of the hose, near the pcv valve or at the back. Thats a dealership Item, think it runs about $30. Grab a motorcraft pcv valve while your there for $5 too. Then clear the codes.

Not sure what sensor 1 slow response is. But I would find that leak at the elbow and replace it.

jbrew has some nice pics in his gallery I think of what that pcv elbow looks like to give you a better idea

 

Also, I believe you have the IAC at the rear of the throttle body. That probably needs cleaning and the hose for it is notorius for cracking and causing a vac leak.

 

AR87,

I had the same problem a little while ago. Turns out I knocked a line off and didnt notice it. Check this out, hope it helps.
https://www.f150online.com/forums/v8...p171-p174.html

 

Well I went home, got some soap water and tried locating the leak. When I removed the cover I could definately hear a hissing sound that I have not heard before. My plan is to remove the TB and clean the IAC while I am at it and while I have the TB removed just check the elbows to see if any are cracked. This also makes it much easier to replace my spark plugs that I was planning on doing anyways. I'll keep you guys posted on what I find.

Thanks!

 

Well I found that I have a huge hole in the elbow behind the throttle body. Bought the parts needed to fix it and will be replacing it tonight. Thanks Toyz and everyone else!