Ok guy so I just got this mail on my 2008 tls auto at 70kmileage
The engine came on but went away the next morning I started it the code was p0174 I got it right after I install my led DRL
And I notice my mpg has dropped to a 11-3rate usually it is like 15-17

 

System too lean (Bank 2) - I do not believe this has anything to do with your recent install of led DRL.

Sounds to me like maybe a vacuum leak or maybe even a O2 sensor. Might have hit something while installing.

 

Nope no leak and CEL never came back on the next day I started it been 2week seen then

But mpg dropped

 

It still sounds like a lazy O2 sensor that is about to/already has died.

I had P0174 and my code came on and off throughout the weeks. I ended up buying a new downstream Bank2 sensor and replaced it. Code hasn't came back since.

If it were a minor vacuum leak, I don't think your gas mileage would suffer as much as you are describing. If the vacuum leak was bad enough TO cause bad gas mileage, I think you would also be throwing a P0171.

 

Sould I do a all data run and see if they work when cold/hot

 

Here's the service manual scan for P0174, if you need it.

 

adjust the valves first then replace the injectors if that doesn't work but valve adjustment has fixed it 99% of the time.

 

is it cold out? my 08 type s does this at least once a month. but its cold out and my car idles every mornign to warm up. only does it in the winter months. i just clear the codes and continue on with my day. mpg is probably a coincidence. ive never noticed a change with that code.

 

needs a valve adjusment

 

been done... even did it a second time to double check.. still does it.