My 97 f250 LD 5.4 is giving me these codes, P0171 & P0174, both banks lean. I have a K&N air intake and in the past my CEL light has come on and I have been able to clear the code by cleaning the Mass air sensor with contact cleaner. Recently my CEL came on but this time when idling the motor a very pronounced miss occurred, its funny, I have a long bumper to bumper commute to work, (1 1/2 hrs) and most of it is idling, well when I let off of the throttle it idles down smoothly for a few seconds then the miss appears sometimes it feels like I’m losing two cylinders. When I apply moderate throttle it smoothes out, if I increase throttle just enough to rise above idle it surges in a very even motion, like I was applying then lifting in an even rhythm even though I have a constant level of throttle applied. This truck has about 210,000 miles on it. At 200,000 I installed a Motorcraft long block. I have replaced one COP but other than that everything else, (injectors, oxy sensors, ect…) is original. Any suggestions?
BTW I just purchased an Innova 3100c OBD 2 code reader to address a CEL problem on my 98 Explorer, (P0302) and it is a very nice unit. It’s on sale at Kragen for $99.00
Thanks for your help!

 

171 and 174 shows a lean condition. Dont know what kind of vehicle you have or engine size to point you in a particular direction. The explorer shows a misfire on cyl 2

 

ok, just saw it--5.4 ---look at the rear of the intake where the pcv hose enters. That elbow is a known trouble spot.

 

Last night I followed the line from the PCV valve to the back of the intake and you were correct, it was rotted clear thru. I took the line out and rapped the elbow with several layers of black tape to make a temporary repair. I reinstalled the line and cleared the codes with the code reader. I then went for a little ride to reset the parameters, at first everything seemed fine, idle was a little high but smooth, I figured it needed to warm up. I drove moderately for about 4 miles before I had to stop for a signal, it idled down to the previously mentioned fast idle for a second or two then went to a normal idle speed but it was missing again. The light turned green and I accelerated away smoothly, no miss at all.
I continued driving for another 10 miles or so with a few stops at signals, same thing; high smooth idle at first then normal idle but with miss but no CEL. As I approached home the CEL came on again.
Today I am going to try to get the hose assembly and PCV valve new as I doubt the integrity of my repair, also the other end of the line seemed a little loose on the PCV valve.
Thanks so much for pointing me in the right direction, I’ll let you know how it turns out.

 

I Had the same problem. I had a leaking PCV valve. Same thing. coad came up back up after i fixed the elbo . I forgot to put the gas cap back on after a fuel stop. i replaced it with a new one. I reset the computer and the coads have not returned. It was a cheap unintentonal fix. you might try it if your PCV valve fix does not work .