3.0 starts intermittently - any guesses?
 

Car is a 2002 A6 3.0, with around 100k miles. I do all maintenance on it, nothing has been touched recently. Yesterday it failed to start several times. If it does start it starts immediately and runs perfectly. When it doesn't start, engine turns over normally, but no sputtering or partial ignition, nothing.

Specifics-the 3 times it didn't start were all after it had been driven, and then parked for 1/2 to 2 hours, so it was still warm. Daytime temps here are in the 80's.

It has not failed to start when cold.
If I shut it off and immediately try to re-start it has always started.

A couple times I came back a few minutes after it wouldn't start and it started normally and immediately-possibly because I opened the hood and something cooled off?

No codes except after a no-start it throws a bunch of cylinder misfire codes.

Once I sprayed starting fluid in the air cleaner box during a time when it didn't start, and it started, then after shutoff it immediately re-started a couple times more. I wouldn't make to much of this though because whatever condition causes the no start could have gone away just conincidentally at that time.

I suspect some critical sensor is on the way to dying, and doesn't like sitting under a hot hood, but works OK when it cools off. What are the likely culprits?

Thanks!

Did you fixed the problem? Did you replaced CTS or ? I'm just curious. x19

I had the exact same symptoms a month ago. Change crankshaft position sensor adapt, it's on it's way ouT. Sensor gets hot due to heat soak after turning off the car or when in traffic. Once it cools down it would work again. I changed mine and it solved the problem. Good luck. It's hard to route the wire on the firewall.

3.0 Audi start up problem
 

Hi there
I had the same problem and it got even worst when its cold outside. I found out that coolant sensor was slowly dying and it wouldn't inject fuel to the cylinders. It controls the start up module it looks like. if your electric radiator kicks in as soon as you start it time to change that sensor. since I did its back to normal