P0171 and P0174 this morning.

[Denali n DOO]

So this morning I got a check engine light showing P0171 and P0174, lean both banks. So here's what the scanner is telling me, engine warmed up to 195*, at idle short term fuel trims changing rapidly every second, both banks. Long term fuel trims staying steady at about 14.83%, both banks. I noticed from recorded info that the long term fuel trims go down to about 6-8% when accelerating and they increase as high as 20-21% when coasting and foot off gas. The light came on while coasting down a hill at about 50 km/h. The O2S S1 v #'s, both banks are also changing rapidly. Maybe not related but 2 nights ago I recorded a weird whiney noise on passenger side of engine (can listen to video). Any idea what made the P0171 and P0174 codes and might the noise be related?
[video=youtube;MwhHfw6_C8U]http://www.youtube.com/watch?v=MwhHfw6_C8U[/video]

 

[Blckshdw]

Copied from OBD-II DTC: P0171 System Too Lean (Bank 1) Since you have that whistling noise, I would lean towards one of the causes that talks about a leak somewhere.

Causes
A code P0171 may mean that one or more of the following has happened:

• The MAF (Mass Air Flow) Sensor is dirty or faulty
• Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
• There could be a vacuum leak downstream of the MAF sensor
• Possible cracked vacuum or PCV line/connection
• Faulty or stuck open PCV valve
• Failed or faulty oxygen sensor (bank 1, sensor 1)
• Sticking/plugged or failed fuel injector
• Low fuel pressure (possible plugged/dirty fuel filter!)
• Exhaust leak between engine and first oxygen sensor

 

[Denali n DOO]

Copied from OBD-II DTC: P0171 System Too Lean (Bank 1) Since you have that whistling noise, I would lean towards one of the causes that talks about a leak somewhere.

Thanks for the info, I'll start by cleaning the MAF sensor with the proper cleaner, checking for vacuum leaks and monitor the long term fuel trims and see if it throws the codes again. So when the long term fuel trim returns to a reading of less than 10% then I would know it's correct?

 

[mrphoenix80]

Since you have that whistling noise, I would lean towards one of the causes that talks about a leak somewhere.

I find a light spray of carb or brake cleaner along the gasket surfaces will help pin point a leak. The engine will change RPM when you hit the spot. Also check near the top of the intake manifold on the right there is an unfinished vacuum port up there. I have seen the "cap" break off a few times causing these codes. And yes under 10% long term is normal. Good Luck to you

 

[Denali n DOO]

Okay, I took the MAF sensor off and cleaned it with MAF cleaner, it didn't look too bad, see pic. When I pulled the intake resonator off I wasn't sure if the little tube going to the top of intake was connected or not. Since the throttle body was staring me in the face I decided to pull it off too and clean it, wasn't too bad a little dirtier on the back side, but it's spotless now. Put everything back together and pulled fuse 10 and 28 for the relearn. After I had the engine running again there was no whiney noise at all, I pulled that little tube off the intake and it made a similiar whining like before so possibly it was not connected. Long term fuel trims are now from -1.55% up to about 7-8%, both banks. I'll continue to monitor the long term fuel trims for a bit but I believe all is good now. I had the carb cleaner but forgot to test around the intake gasket. Thanks for the help guys