I am at wits end. Any he
lp would be greatly appreciated. I have a 2004 f150 with a 4.6l. The other day it started idling rough and gave me 2 codes bank 1 sensor 1 and bank 2 sensor 1 stuck lean. I did some looking around and found a vacuum leak on the pcv elbow on the back of the throttle body. I replaced the entire hose and the pcv valve. Now the stupid thing is giving me 2 new codes bank 1 sensor 1 stuck rich and bank 2 sensor 1 stuck rich. I also replaced the MAF sensor. Any ideas where to look would be wonderful.

 

Make sure the MAF is properly plugged in.
Post any and all existing codes in your reply. Any pending codes?

 

I checked and the MAF is plugged in completely. The codes are P2196 and P2198. Those are only 2 codes. Not sure if this helps or not but it runs fine cold,after it warms up is when the issues arise, but only at idle not while driving at highway speeds.

 

You have the highest vacuum at idle , the low rpm means any leak has a big effect at idle . Check your purge valve on firewall to see if its leaking thru. If its letting gas fumes in when its supposed to be deenergized it will run rich (Common problem) You can try to

blow thru it or use pressure air to test . . Also check vacuum side of fuel rail sensor . If that diagram goes bad it will suck fuel thru it . You can pinch it off for test .
2004 vac connection on intake manifold passenger side nearest firewall is a bad design it falls out and is difficult to get back in . 05 's they put a metal wye connection by brake booster and plugged manifold .
Another common problem is to get hose lines mixed up on passenger side , One is fresh air throttle body fresh air into passenger valve cover. The other is vacuum to purge valve on firewall ,this causes some weird symptoms .

 

Thanks, I will try the purge valve. Just doesn't make sense to me that it would throw lean codes and then after cleaning the MAF it throws rich codes which is why I replaced it, thinking it was bad. Very frustrating.

 

Did you unhook the battery or reset the kam after you fixed the vacuum leak? I would think the PCM should reset the settings itself after you fixed the leak, but maybe not if it was adding a ton of fuel to compensate for the vacuum leak and now it's repaired it's showing rich.

You might want to unhook the battery for a few so the PCM resets to default settings and see if it resolve on its own.

Also the engine doesn't run in closed loop from a cold start, it always starts in open loop mode until it gets close to operating temp then closed loop kicks in, so it would make sense that it runs better at a cold start it's running in default settings with no control loop at that point.

 

My guess is that it's running rich now to bring the long-term fuel trims back to approximately zero. But if you run it awhile to allow the long term trims to stabilize, and it still runs rough, it's something else.

Let us know if the problem persists.

 

Thanks everyone for all the different things to check. I have tried everything and nothing has worked yet. Not sure about the purge valve check yet. I ended up breaking a connector on one of the vacuum lines so I have to get a new connection tomorrow. Hopefully that is the issue but won't know until tomorrow. I will let everyone know the outcome.

 

Nothing has worked so far. I've tried everything. At idle both banks short term fuel read -1.6 and long term fuel read about -2.0. driving at 30 mph both banks short term fuel read about 1% either side of zero and the long term fuel on both banks reads -19% to -21%. Really getting frustrated and annoyed with it.

 

I find it hard to believe, but is it possible that both upstream O2 sensors are bad? I'm running out of ideas. Don't really want to bring it in but I might be have to.