Car starts, then stalls. Audible relay clicking afterward.

[nicepants]

I went to start my 2004 A4 3.0 Quattro this morning (about 65-70 degrees out) and it cranked, started, and ran for about 3 or 4 seconds. Then it abruptly died. Afterward, there was a relay-like clicking from behind the dash, and noise that seemed to be coming from the vacuum system. No check engine light (however, now I see that the check engine light and ECM *may* be flashing, I can't tell) and the car checks 'OK' prior to start and the engine firing. Doesn't seem to be an immobilizer problem, tried my other key and it seems to display the same symptoms.

Additionally, the clicking is also audible and occurs just with the car in ACC before startup.

I have a VAG-COM but it keeps displaying communication errors, and I haven't gotten further than that.

Lastly - and not sure if this is significant - I just removed the radio prior to trying to start it and showing this issue. The radio seems to be fine, and I'd imagine this is unrelated, but it did occur immediately after I worked on it.

Any help majorly appreciated. The car is completely immobile right now and I'm at a loss.

[nicepants]

update: now the car won't even start. Click click click goes the dash, fan turns on as well (which is strange, considering the car is cold).

Again, seriously distraught here and not sure what to do.

[nicepants]

updates just incase anyone ever checks this thread - here are the codes my V-checker is displaying (finally got it to work):

16684.P0300 Random/Multiple Cylinder: Misfire Detected
16688.P0304 Cylinder 4: Misfire Detected
19537.P3081 Engine Temperature: Too Low
18010.P1602 Power Supply (B+) Terminal 30: Low Voltage
17978.P1570 Engine Control Module Disabled
18043.P1635 Data Bus Powertrain: Missing Message from Air Conditioner Control
18011.P1603 Internal Control Module Memory: Checksum Error
18058.P1650 Data Bus Powertrain: Missing Message from Instrument Cluster ECU

A few of these make sense: my gas gauge and trip calculator (the center readout) have been acting wonky, I attempted to reset it by pulling fuses 15 & 28 (I think, I'll have to check). I'm guessing that caused the ECU code. I also disconnected the battery in an attempt to reset the ECU, and pulled several fuses and relays (without the car on, however) to check their health.

Does anyone have a clue or any insight into what I should be checking into next? Any help immensely appreciated.

[nicepants]

Another update: 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?

[imnuts]

With the last codes you posted, I would look into the wiring going to the ECU, particularly the power wires. You may have a loose or damaged wire or wires causing your problem.

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