DA8

Thing is I have had the problem as long as I had the car. When I replaced the MAF years ago it had no effect to solve the SAI issue then, why’d would it now?

MP4.2+6.0

Skimming through this again, did you ever confirm the basic air pump function? That is, spin it up w/ either VCDS or by jumpering the terminals w/ 12V?

If the CEL is going back on after two cold-hot-cold driving cycles, it is basically reporting it sees a very consistent problem. If that number of cycles is more fleeting/variable, it is something more subtle or subject to other conditions.

DA8

I verified good operation of the air pump, and ruled out replacing it due to the $500 cost. Then later, at my whits end I replaced the perfectly good air pump with a new one to rule that out. I also replaced all air hoses. The air hose that leads to the left combi valve was a bitch to replace because it routes under the rear coolant line and under the throttle body between the block and head.

There is not one SAI component I have not replaced. Yet the SAI insufficient flow code persist. Yes, it comes up about every 2-3 drive cycles on average and I just clear it immediately with my BLU DRIVER code reader on my phone.

dvs_dave

For what it’s worth, I had this error and it was because of a failed combi-valve. The vacuum diaphragm had failed. Easily diagnosed with the aid of a hand vacuum pump.

What was unexpected though was that the new one fitted failed in exactly the same way within a week of the initial repair. It was replaced again (under warranty) and has been good ever since (around a year so far).

Point being that you’ve replaced everything, but that assumes that everything you’ve replaced is still working as it should. Given my experience I wouldn’t be surprised if one of your “new” combi valves, solenoid, or vacuum pipes have actually failed again. The system function is very easy to test with a hand vacuum pump. If it won’t hold a vacuum, and/or you can’t hear the combi valves operating, you’ve found the culprit.

culi

Mind if I chime in? I have a 3.0T engine, but I think the same concept applies. If after replacing the combi valves, hoses, and secondary air pump doesn't solve your problem, you might have a clog secondary injection port. The port is what the combi valves attached to. You have to clean that out the port that run the whole length of the engine block. Also you have to clean the ports out from the side. The exhaust manifolds needs to come off to access those side ports. See these two videos for reference.

maxandtara

Looks like one more thing to add on the to do list when you do the timing belt.

Does this apply to port injected engines ?

Or does this only apply to Direct injection and Turbo engines ?

MP4.2+6.0

Check carefully, and definitely don't assume. Predecessor 4.2 used in C5 A6 and D2 A8 had no auxiliary ports for SAI. But, the 3.2 V6 that preceded the 3.0T did, and was sort of ground zero for early direct injection fouling on Audi motors. 3.0T by the way is supercharged rather than turbo as a nuance.

Thus, it may just be a V6 thing. You need someone with specific experience on the Audi heads for both the port and direct injection V8's used in D3's to confirm either way.

dvs_dave

Definitely not a known problem with the D3’s, any engines, and only worth the pain of investigation if you’ve literally exhausted all other SAI system fault sources.

DI engines are sootier than port injection engines, so there is that. But knowing how the SAI system works, I’d say this is a consequence of ignoring an SAI system problem for a long period of time. It’s not possible for exhaust gasses to flow in any significant amounts through the SAI ports, unless the combi valve for that port is stuck open. And there would likely be other symptoms manifest before it gets to a point where the ports are coked up. Namely an SAI pump failure due to it being full of water/heavily corroded. This isn’t because it sucked up a load of water, it’s because a combi valve was stuck open and exhaust gases have back flowed through the pump, and the moisture has condensed in the pipe work and over time collected as a fairly corrosive mix in the pump assembly as the systems low point.