Cold start diagnosis

[C6NVS]

Hi all,

Recently having intermittent problems on start up. Occasionally, on cold start the car will turn over and fire, but revs quickly die down and it stalls. After a few more tries and a very slight dab on the loud pedal to entice it to run, it will stay running, but it idles like it is on 4 cylinders and eventually the fuel smell is apparent before I decide enough is enough and shut it down.

I'm guessing something to do with ignition/timing /misfiring mix up (well done Einstein!!!), but I don't know enough to diagnose further or to test a completely dead MAF or Lambada. The air box is on securely, and the only way I seem to be able to temporarily fix the issue is to disconnect the battery and wait 10 mins before it randomly starts without a hitch. This is only the second time in recent months, but the symptoms are exactly the same both times.

Any ideas on what might be the cause from my description? I could add to the list to possibly include Limp Mode (but no light), wiring issue, bad fuel (different fuels on both occasions), but I'm scratching my head.

I'll vag it when I get a chance and post results (probably not till next week), but keen to hear initial thoughts as I''ve only attempted to diagnose when I am in a hurry to go somewhere.

Thanks.

[slimmyreed]

I had similar issues with my car when the airbox wasn't seated properly. Make sure it is sealed properly where it sits in the inlet manifold. You can confirm if it is the mafs at fault by disconnecting them. When they are disconnected the car will run a basic map, and should run ok if it is the mafs at fault. However you don't want to leave it like that for too long, as the car will over fuel, and you risk burning out your cats.

[Shoppinit]

These things are a nightmare to diagnose without a vagcom. If you think it's the MAFs, you can try to disconnect them and see how the engine runs. That way it'll run on limp mode. If it runs better with the MAFs disconnected, it might point to a dodgy MAFs.

Actually, the RS6 are prone to vacuum pipes perishing. Check the vac pipes, big and small. The master cylinder vac pipe can perish, too.