Hello,

few days ago my idle got rough, check engine light came on, and bunch of codes showed-up... I cleared the codes and car ran smooth again for a day. Then again same thing.

When I drive all seem nice and smooth, only idle is the problem so far.

Anybody experienced something like this and knows the cure?

I don't think it can be related to spark plugs or coils, they just don't go bad all together.

My first reaction was that oxygen sensor needs replacement, but I see both banks too lean at the same time - also unlikely that both went bad at the same time.

P0171 System too Lean (Bank 1)
P0174 System too Lean (Bank 2)

What are the common causes for this? Any ideas?

Thank you!

 

Very common. 2 things to check.
1. Air intake tube between air filter box and throttle body will split on the underside of the bellows. Replace the tube if needed. Don't put a bandaid on it as the engine bay heat will put you right back in the same boat.
2. Remove air flow sensor from top of air filter box, spray brake or electrical cleaner all up inside it and preferably blow it out with compressed air or let dry.
Go back and clear codes after you fixed what was wrong.

 

Thank you!
While tube had no cracks, you sent me on the right track. After inspecting tube and connection to throttle body I started the car and there was noticeable hissing sound. The problem was - broken breather line(in the picture).

Fixed it with 'strong Band-Aid :-) ' and cleared the codes. Idle is back to normal and no more fault codes. I love it when problems get fixed in this manner!

Thanks again!

 

There ought to be not even a tiny leak. Snag is that a leak you can hear is usually quite big whereas the tiny ones you cannot hear. You can use an OBD tool with live data to check the fuel trims and they will show even tiny leaks. Such tools start from about $5-10.

 

I do have an OBDII 'thing' that connects to my phone. Could you tell me what 'live data' would tell me that there is a leak? I think it will help everyone here if you could explain how to find these tiny leaks using OBD data. ( I am using 'Torque' application if that of any help.)

Thank you.

 

Look for long term fuel trims LTFT. At idle they should be low single digits.