2004 Avant Quattro 6MT stalling after running 10-30 seconds
 

Car will start, especially after sitting for a long period. It'll be seemingly perfect, then like someone threw a kill switch, it'll die. Then the relay clicking will start. It's running super-rich, the smell of gas is nearly overwhelming afterward. These three codes seem to be appearing:

18043.P1635 Data Bus Powertrain: Missing Message from Air Conditioner Control
18011.P1603 Internal Control Module Memory: Checksum Error
18010.P1602 Power Supply (B+) Terminal 30: Low Voltage

But sometimes, there's not even a code thrown. The ESP light and CEL light will blink with each sound of the relay closing, but then they'll disappear. The traction control light will sometimes come on and stay on.

As soon as the relay starts clicking, my V-checker will display "Comm error" and will act like it's disconnected from the ECU.

Is this an ECU problem? An ECU power problem?