P0174
 

P0174 - bank 2 running lean...

Two months ago I had the car serviced for P0174 and P0171 codes, which they traced to the air filter that had been eaten away by a mouse. They replaced the air filter, and cleared the code. No trouble for 100-150 miles or so. Now P0174 comes up, and I want to get some ideas before I go to the dealer, from what I've heard it can range from a vacuum leak to a dirty MAF to bad O2 sensors. I wanted to know what to start with first, as I don't want to have the dealer waste my time or money in case they misdiagnose it, considering this code can be caused by a variety of things. 60,000 miles, 2004 X3 3.0i.

Any advice would be greatly appreciated.

Is the truck running any different? If it's stumbling or down on power I would start by looking at the maf and checking all my vac lines. You can clean the maf with spray cleaner and reinstall to see if that helps, but there's a chance it's failed in which case you will need to replace it. What model X3 do you have so I can look and see if I have any notes on it.

ECS Tuning

It seems to be running fine. There is a clicking sound coming from the engine bay that I did not notice before though, I don't know if that will help.

It's a 2004 E83 X3 3.0i, engine is an M54B30.

Hi,
You can try to clean the MAF sensor first. make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling.
If it doen't work, inspect all vacuum and PCV hoses, replace if necessary.
If problem also exists, check for a dirty fuel filter and proper fuel pressure.

Good luck.

The clicking sound is probably the valve in the intake manifold (the one that adjust the manifold length... the proper German name escapes me now): it's common.

Replacing it on the X3 is tight, but can be done. The one thing you'll have to be careful is when you remove it not to have the shaft falling in the manifold. The shaft can come loose and when pulling it out might fall down. Move slowly and be patient.

The running lean is a vacuum leak: very common too. Two things to check:
1) the branch in the manifold going to the idle control valve cracks. Replace it
2) the crankcase ventilation systems leaks: in this case there's not really a definitive way to diagnose it. You'd have to replace the valve/separator and the plumbing around it.
I normally start with the manifold, and if the problem comes back replace the crankcase ventilation system.

Dirty MAF, bad O2 sensor or even failed cat are normally bad diagnoses and very very rare causes of the symptoms you have...

I hope this helps! Let us know...

They found a torn throttle boot, and now clicking sound is gone. They also replaced vanos high pressure line and oil filter gasket, as those were leaking, but problem solved!

That's dandy!!!! Now you should be set for many many miles...