Here we go again. Took a hour long trip (with A/C on). No problems. Turned car off. Went into a store. Came out 15 minutes later and car wouldn't start. Came back an hour later and no problems. I've replaced plugs, fuel filter, air filter, checked wires with multimeter (all have same resistance). Also, cleaned and dried the TPS connector which seemed to have water in it and two oxidized pins. Could it be the temp sensor? Maybe the cat? This seems to happen after it rains and when it is very humid. Tomorrow I will check the TPS again for water. Any thoughts are much appreciated.

Does the starter turn slowly when you turn the key? Or does it turn fast like usual but just no ignition?

No, it isn't the starter or battery . . . or the alternator. This problem is specific to hot starts. Fires right up and idles smoothly when cold.

Heat soaked crank position sensor. If you can't remember when the last time the crank position and the speed sensor were replaced then replace then now. They are both mounted on the same bracket (cost about $140.00 to $160.00 each). Hard starting when hot is a known problem with these sensors. Being only a couple of inches away from the exhaust manifold the heat tends to fry these sensors.

When the engine doesn't start pull the DTC (Diagnostic Trouble Codes). They will blink out the code for a Crank position sensor problem (2112) flywheel pin missing .

The crank position sensor sends a signal to the ECU (engine control unit) to let it knows when the number one cylinder is approaching TDC, which cause the fuel injectors to fire in sequence. Your injector aren't firing because the signal is missing. This is a magnetic sensor which reads a pin on the flywheel. The magnetic property of the sensor decrease as the temperature increase. As the pin from the flywheel passes over the sensor it distrub the magnetic field which is used by the ECU.<ul><li><a href="http://www.sjmautotechnik.com/ecufv8.html">DTC Quattro V8</a></li></ul>

Sensors are the same as on my '90 200, same symptoms when mine failed. My manual has a test, testing resistance I believe. Find the sensors, mine are on the left side front of the flywheel about 10 or 11 o'clock (looking forward). Two wires come from a row of connectors on the right, upper firewall to the two sensors. Next time it happens, get a cup of cool water and pour it on them, it should start right up. Good luck!

not sure about the V8 setup, but in the 5k it would be a probable cause.
Zsolt

In addition to being a great resource site for Audi, Scott's site also sell Audi parts. You could also search any of the web sites selling audi parts. I believe that we should support sites such as Scott as much as possible.<ul><li><a href="http://www.sjmautotechnik.com">Scott's site sjmautotechnik</a></li></ul>

Try a worldpac dealer like bimmerparts or zzmotors. Don't know how their prices for the reference sensor compare to a dealer's though. Sometimes their prices are lower and sometimes not.

i have the same problem with mine. I have been told that it is the crankshaft position sensor getting heatsoaked by Max at AVS in Wa. It will still turn over but if you look at the tach it doesnt budge. When i had the timing belt done at the dealer they told me it was either that or a coil getting heatsoaked..
I would start with the crank sensor. Get the engine real hot then shut it off and wait about 5 minutes and try to start it again. When it wont start try using a multimeter or scope and backprobing the crank sensor... unless you know which pin it is at the cpu.

<center><img src="http://pictureposter.audiworld.com/36396/audiv832a.t.jpg"></center><p>
Location of crank and speed sensors.<ul><li><a href="http://pictureposter.audiworld.com/36396/audiv832a.jpg">Crank and speed sensor</a></li></ul>

If the tach doesn't bounce then it is the speed sensor.

Both speed and crank position sensors are mounted on a bracket behind a heat shield. It is wise to replace both of them at the same time. Heat over time will destroy these sensors.

If the speed sensor is malfunctioning then the engine will not start and if the engine was running then it will die.

If the crank position sensor is malfunctioning, then the car will not start, but if was running then the ECU will default to a value when the engine was started (engine continue to run).<ul><li><a href="http://pictureposter.audiworld.com/36396/audiv832a.jpg">Sensor location</a></li></ul>