Before ordering the Combi valve, I looked at the vacuum lines coming out of it on Saturday. Sure enough, the intake side fabric was frayed at both ends and actually broken in the middle and at the end under the manifold. Replaced with some red (+5 hp) silicone tubing. No CELs in two cold starts. Like the old saying goes, start with the cheapest, easiest solution and go from there.
If the vac lines had checked out ok, the following info that ModifiedA4 has posted many times would be useful:
"In the event you have an A4 1.8T with engine code ATW with the DTC of 16795 - Secondary Air Injection system, Incorrect flow Detected, a leaking Combination valve could be the problem. A leaking valve causes exhaust gas to enter the secondary air system. The water from exhaust condensation travels through the entire secondary air injection system and if the temperature drops below 0 degrees Celsius the water will freeze. In most cases the water causes the air pump to corrode. Inspecting the combination valve will reveal the problem. If the Intake side of the valve is black, exhaust has entered the secondary air injection system"
Combi valve (06B 131 101 H) runs ~$120 at 1stvwparts.com and then the Secondary Air Injection pump gets expensive.
My car had this problem twice during it's warranty period. 1st one was on the house...second one was starting to become an issue, but the service manager couldn't confirm it (I could if I dropped it in chipped mode...because boost was bleeding out...somewhere). I never found the source, but more than likely it was exactly what you described. Where is this line attach to the intake manifold?
2005.5 A4 Avant 2.0T Quattro 6MT
APR 91/93/100 | APR Exhaust | 19" BBS RS-GT's | Carbonio | Hotchkis | Partridge-in-a-pear-tree
2006 TL on the block
2001 S4 sold
2000 A4 sold