Hi all, 2014 Q7 with about 94k miles on it. It's been having some odd starts intermittently where rpms bounce or hunt for a second or two before settling in. Check engine ultimately came on. I'd pulled codes on it before dropping off and found the P0491/ P0492 which are insufficient airflow in secondary air injection system. Dealer also showed me two other codes that have been intermittent, P1559 throttle valve control module malfunction that they explain as the valve getting briefly stuck, and P0456 which is a pressure drop in fuel vapor recovery.

Dealer recommends $1500 worth of cleaning the air injection bypass valves (which of course requires a/c compressor removal to get to them since everything Audi designs is a nightmare layout), cleaning throttle body, and wait and see on the vapor thing because finding if there's a leak this small would be very intensive but will swap the gas cap to see if it's just the gasket on there.

My understanding of the secondary bypass is it just feeds additional air through to the exhaust manifold to influence the burning of more fuel on the cats at startup to heat them up faster, but otherwise it shouldn't result in difficult starts or running issues. Is that accurate?

On the throttle body, that sounds more likely to be the weird start culprit. Does cleaning usually resolve or am I just prolonging replacement by pointlessly having them clean it?

Thanks!

 

Do you have the 3.0TFSI gas? If so there is a TSB for them to fix the secondary air issue, carbon clean.

https://static.nhtsa.gov/odi/tsbs/20...53120-9999.pdf

I would have them do the free work, then see if the interment codes come back.

 

Yep 3.0 no supercharger gasoline. The q7 is 2014 94k miles though, so way past what was only a four year 50k mile warranty at that model year.

I believe that TSB is the one the dealer referenced though as they sent me a video that I recognize part of from what you posted, and it confirms "If vehicle is outside any warranty, this Technical Service Bulletin is informational only." I'm inclined to not have them do it if this doesn't impact starting and drivability, just minor change in startup emissions, given the cost of labor being $1000+ for this.

 

Well dang, I didn't notice that part.
It is easer to do on the Q7 though, than the other modes with the 3.0T. We at least have a little room in front of the engine to work. I've seen this done with a giant drill bit, but that requires putting the car in service position (taking the front off) and also by using a pressure washer which you might be able to sneak one in on the Q7.

 

FWIW, I'd start with low-hanging fruit that's easy to do and supportive of overall goal, rather than taking it apart. Smarter, not harder; basically an intake system tune-up. REMOVE the Mass Airflow sensor/ clean it off car. Replace old engine air filter at same time. Get an intake cleaner (probably couple bottles) spray product from Liqui Moly or your preferred vendor...follow directions exactly to clear deposits from the intake system, throttle body, intake valves, etc. I'd also verify when fuel filter was replaced last (yeah, change it), and introduce a high quality fuel system/concentrated injector cleaner...following each product's directions are very important for reaching desired results. If you are close to oil change, use an oil flush product to remove varnish/deposits, and then refill with an excellent oil, such as Liqui Moly, Amsoil, Motul, etc. I'd stay away from Castrol or the VW/Audi branded, OE oil, but that's just based on how my cars run on those oils...very noisy.

I'd bet you rapidly see some positive results once you clean out mass airflow sensor and all the restrictions and garbage deposits throughout the intake tract, air filter/fuel filter, plus clean those injectors. You might spend what, $100-$150 on filters & chemical additives/cleaners/flush products; call it $200 + if you spring for the oil change kit, and do it all yourself. I really like the complete line of Liqui Moly products in our cars, as they work.