Rough Idle 3.2L XC70 - Lean fuel trims

[LRNXC70]

Hi all,

New to the group and looking for some input on a rough idle on my 2010 XC70 3.2L.

Not throwing any engine codes, but running very rough at idle. Runs smooth above idle.

STFT on bank 1 & 2 showing between 25-35% 
LTFT on bank 1 &2 showing around 6% 


Plugs removed and verified lean (very white)


My initial thought was intake leak but I’ve had the intake manifold off and all intake pipes off twice looking for leaks. All connections tight, no cracks in hoses, gaskets all look good.

 
Occasionally after a high rev up to 4000 rpm, car settles and idles smooth for a 5-10 mins with fuel trims around 0%. From what I’ve read, intake leaks aren’t usually intermittent.


Replaced MAF twice now (first one was not reputable brand, second one is OEM Bosch. No fix.

Replaced fuel rail pressure sensor with OEM - no fix.



Both O2 sensors (pre cat) showing very low volts but not fluctuating (around 0.1) - also indicating lean. If I disconnect o2 sensors with car running, nothing happens. 



Questions:
- Could it be O2 sensors gone bad? If so, weird that both would go at the same time? (Both reading exactly the same). But if they are both reading lean, wouldn’t they be telling the ECM to add more fuel and therefore plugs would look normal?

- Could PCV cause this rough idle? I don’t hear any hissing.
- Possibly exhaust leak pre O2 sensors? Would I hear an exhaust leak?
- Fuel pump?

Any help would be greatly appreciated!

[scot850]

Are you getting a cat efficiency low reading at all? The bolts on the cat to downpipe like to fall out. Hard to see.

Neil.

[pgill]

Here is what I would do

1. disconnect the MAF and start the engine (it should be able to run using the MAP ONLY)

2. Check the fuel trims if it changed significantly then look for an intake leak or go to item 3

3. no change in fuel trim at idle on MAP only then replace the fuel pressure sending unit.

good luck

Paul

Fuel Pressure sensor information
https://www.freel2.com/forum/topic39122.html

False Air intake leak information