P0171 and P0174 caused by missing oil filler cap?

[shadow460]

Topic says it all. I fueled up in the bitter cold yesterday and checked all fluids as usual. It needed a little oil so I added some. This morning I got a CEL with P0171 and P0174. I looked under the hood to check vacuum hoses and saw I'd left the oil cap sitting on the washer tank. After putting it back on, long term fuel trim dropped from 23% plus on both banks to 14%.
Since the oil cap seals against the same valve cover the PCV hoses that normally leak seal up to, I assume leaving the cap off is a good way to cause a vacuum "leak".
The CEL is still on. Should I use the scan tool to kill it or will it eventually turn off by itself if the problem is fixed?

 

[Kansas Gary]

If you have a scan tool I would turn it off and see if it relights later on.

 

[shadow460]

Yeah, I went ahead and wiped that offensive yellow thing off my dash. I need a reason to drive to Edmond and back anyway. If it's gonna light, it'll do it on that trip.

 

[FordandPolaris]

Computer holds onto the code regardless if it has been repaired until it is reset. PCV mean positive crankcase ventilation or something near that, so leaving the oil cap off would in turn not allow for any such positive pressure to build. I think it would be safe to assume the cap caused the issue.

 

[toms89]

Yep..

Controlled vacuum leak via the pvc system. Un-metered air entering the intake creates lean condition. Generally the pcv pulls air through the engine via a "fresh air" hose attached to the opposite valve cover. This gets it air after the mass air meter so it is "metered air". With the oil fill cap off you create a source of un-metered air to be introduced instead of pulling air through the mass air sensor.

 

[shadow460]

lol, I feel like such a bonehead for leaving that off. But hey, the light did its job. It said "Check Engine," so I did, and I found something wrong!

 

[FordandPolaris]

lol, I feel like such a bonehead for leaving that off. But hey, the light did its job. It said "Check Engine," so I did, and I found something wrong!

Don't worry, I lost my brake fluid cap the same type of way and for about 2 years only had a thick piece of tin foil and one very gross looking rubber band covering it up... Only after I replaced the master cylinder cause the old one was failing did I get a cap again haha. It happens.