Recently my XF Supercharged developed a rough idle condition, upon investigation the cold air intake tube was severely cracked. I replaced it w a Mina intake tube, the rough idle condition seemed resolved. After a few days of driving Check Engine light comes on, throwing System Lean P0171/P0174. I completely removed the intake, and reinstalled to make sure nothing was loose, cleaned both MAFS. Any thoughts would be appreciated. Thanks.

 

does it always idle rough, is it worse on a cold start vs idling with a warm engine?

 

Need to check for unmetered air coming through intake. I would check the PCV valve on right side valve cover. Seen them leak and cause this code.

 

The rough idle condition is almost non existent. What i see on a cold start, or any start for that matter the RPMs bounce a couple hundred rpms only for 2 to 3 seconds. I don't know if that's normal. After those first few seconds the idle drops and is near perfect, no engine stutter etc. Check engine light stays on though. Thanks.

 

Before the cold air intake tube replacement the rough idle was very noticeable, but no check engine light.

 

Its probably one of the following:

1) you have an air intake leak somewhere (check for leaks)
2) you don't have enough fuel going into the engine (check fuel filter, injector, pump, rail pressure)
3) the MAF sensors are not reporting the amount of air correctly (replace MAFs)

 

I am definitely in agreement with that. I feel it still has a vacuum/air leak, or possibly a fuel delivery issue. It is going to the shop tomorrow for full diagnosis. I myself have given up, lol. Need a more detailed read out than the generic codes of a basic obd2 unit.