My Q7 is 18 year old and with 88k miles. This year my Q7 needs a smog certificate before it can be registered to drive in CA. It’s been sitting outside for a long time, I had P0174 Bank 2 Fuel Trim too lean popped up, also P0456 Evap has small leak. The gas mileage keeps going to 14MPG, even on the freeway. The car doesn’t run smooth and down/up shift on transmission not smooth due to losing power.
After reading online, there are quite a few causes which one of them I don’t want to think of PCV valve under the intake manifold.
- Replacing the Air Filter didn’t help.
- Bought MAF cleaner to clean it and it didn’t help either.
- Bought a $12 gas cap on Amazon to replace the old cracking one and it fixed the P0456.
- Bought a $35 MAF on Amazon, replaced and it passed. The engine runs smoother, shift gear up/down better, gas mileage better, more power.
The MAF part number 03H906461 and 0280218175 for 2008 Q7 3.6L.
I’m very happy that I don’t have to replace the PCV under the intake manifold, it would be a lot of work.
