Hey guys, don't post much but I know forums are the place to go when looking for some knowledge about specific cars

Anyways, I drive a 2001 Allroad (pretty much A6 avant) with the 2.7t engine.

For the last month or so, I've had an INTERMITTENT problem with starting my car. First off, it doesnt matter if it is 20 or 80 degrees outside, so weather does not seem to be a factor. And this only happens about 1/5 start ups after the car has been sitting overnight or long enough to completely cool down.

So heres what happens (when it does happen),
-I turn the key in the ignition, and nothing happens. After a few more tries, the car will attempt to start up, then die within a couple seconds.
-After each cycle, the car will attempt to idle for just a bit longer each time. However, the RPM's usually do not go much higher than 500rpm, with severe shaking and "puttering".
-Finally after 10-20 attempts, the car will start up without dying. Again the RPM's stay well below the normal cold start-up range and there definitely seems to be misfiring.
-If I press the gas pedal, the car will stutter and struggle to raise the RPM's. After a few minutes of warming up, everything seems to be okay and run as normal.
-Also, I'm pretty sure there is a slight gas odor and I swear on one occasion I saw a little bit of smoke from the exhaust in the first few seconds. So this must mean either the engine is flooding out for some reason, or that is just the result from the normal amount of fuel going into the engine finally being burnt off after the car finally starts up and stays running.

Yes, the CEL came on and the only code I pulled was the "Coolant Temp Sensor...". I bought a new sensor and installed it right away thinking it'd be a simple fix. However, the problem came back 2 days later and the CEL is throwing the same code.
I know there is a slight chance that the new sensor is bad too, but not likely. Also, I know that one problem can cause others like a chain reaction, causing the computer to throw a code that is irrelevant to the source of the problem.

I went ahead and changed out the fuel filter, thinking that was a possible issue....but that still did not fix the problem. I also replaced the spark plugs...again, no fix.

The city I currently live in does not have an Audi dealer, or any shops that specialize in VW/Audi vehicles. There is a VW dealer in town, but they said they weren't sure if they would be able to diagnose the problem since VW vehicles do not share the same engine I have. So basically I am hoping someone here can guide me in the right direction to pin-pointing the problem so I don't have to drive 350 miles to the closest shop I know of capable and trustworthy enough of working on my car.




(idk if this is allowed or not but I am going to make copies of this thread in the A4, A6, and Allroad forum sections since all 3 vehicles share the same engine I have...2.7t)

 

From your post it seems like it cranks over OK, (doesn't seem to be grunting, groaning trying to turn over the engine) especially since you are saying that you are cranking the thing 10+ times. There is a possibility that you have either a fuel pressure regulator bleeding down, or since you said that you believe you smell fuel, you may have an injector leaking/bleeding down. If your fuel pressure is too low you will have starting problems, and issues with getting it to idle, until the pressure builds up. I also noticed you did not make any comments or reference to issues once it's up and running, which if it were a fuel pump or blocked filter you should notice issues when the motor is in it's powerband going down the road. The "fun" part in this is access to measure and monitor the fuel pressure after overnight or long "cold" soaks. There is not a service port on the fuel rail, but in order to monitor this condition you have to find a way to tap into the fuel line to attach a gauge. If you see a slight drop (couple pounds) in pressure after an extended off period, that's OK. if you have a significant drop in pressure you need to search for the leak.

 

the symptoms are consistent with a bad ECT. I dont know much about the 2.7t, but some engines have two temp sensors, so make sure the one you replaced is the one that will throw a CEL

 

I am pretty sure there is only one temp sensor, but i'll definitely look into the possibility of there being a second. And ECT...whats that? (hah i sound like a noob)

quattro0001 - Once the car is up and running, I have to wait at least 2-3 minutes before I can put it in gear and drive. It seems the engine has to warm up a bit and "regulate" everything before I can accelerate, otherwise it will stutter and shake or stall.
Fuel pressure regulator has crossed my mind - but if that was the case, wouldnt this problem occur after every "cold" startup?

I am almost positive everything is stemming from something electrical related, whatever that may be...especially since again, this issue is only intermittent.

EDIT - Duh! haha ECT=Engine Coolant Temp Since the sensor is cheap enough....I might as well spend another $10 and replace it again. Just gotta make sure I catch the coolant this time instead of let it go down the driveway. Pentosin isn't exactly cheap

 

This applies to codes P0116 thru P0119

Since you didn't give the exact code it is possible that the wiring has an issue and not just the sensor.
Ensure you have replaced the sensor with a green one (P/N 059919501A), not a black one which has been confirmed by Audi to cause problems.
Also depending on the code it could be the thermostat, but unlikley.


16501/P0117 - Engine Coolant Temperature Sensor (G62): Signal too Low
Possible Symptoms

* Difficulties with starting a cold engine.
* Starting the engine when engine is warmish or warm, idle rpm immediately is 1200 - 3000 rpm.
* RPM at idle is irregular.
* With all engine temperatures seldom idle rpm will vary between 900 - 1000 rpm.
* With engine warm (90 °C) the engine temperature suddenly drops (70 °C) and slowly comes back to 90 °C.
* Bad acceleration during warming up.
o Diesel: an indication is extreme long time burning time of the glow indication light.

Possible Causes

* The electrical signal coming from G62 is too low
* Wiring and/or connections faulty (short circuit?)
* Engine Coolant Temperature Sensor (G62) faulty

Possible Solutions

* Check wiring and connections
* Check / Replace Engine Coolant Temperature Sensor (G62)

Special Notes

* In MY 1995-2002 (?) in Europe at VW-cars the G2/G62 had the bad reputation of breaking down often. The default G2/G62 is black and all replacements are green.





17704/P1296/004758 - Error in Mapped Cooling System
Possible Symptoms

* Cold start issues

Possible Causes

* Coolant Temperature Sensor (G62) faulty
* Coolant Thermostat faulty

Possible Solutions

* Check Coolant Temperature Sensor (G62)
* Check Coolant Thermostat

 

Thanks for the detailed info swilky2000!

Okay so I took a simple approach, and purchased another coolant temp sensor from the VW dealer in town. I called Audi first to make sure the part numbers matched up.

The first sensor I bought was from Autozone...and I figured there was the chance it was defective.

So after spending the extra money and buying the OEM part, I installed it about 2 hours ago. So far the CEL has not come back on and everything seems to be running okay. I'll keep my fingers crossed for the next few days before I confirm the OEM sensor is all it needed.

 

UPDATE!!

So last night I was driving to campus to go study at the library....shortly after picking up a friend to go study with, I was telling her about how I just changed that sensor to an OEM one. Literally 10 seconds went by and the CEL came on!

I have not had a chance to check the code yet, but this morning I experienced the same symptoms! Car did not start-up until a few attempts and once it did finally start, the idle was the same low/rough idle until warm up. So obviously switching to an OEM part still has not fixed my problem.

Before I installed the new sensor, I inspected the wiring and harness that plugs into the Coolant Temp sensor...everything looked to be in good condition.

UGH! Now I am pretty much stumped! Now it's either gotta be the wiring or worst case, my ECU......

 

Did you ever figure this out? I'm having the same issues with my Allroad right now amidst corona lockdown.. Mine is a touch worse though but doe's seem thoroughly random.. Have killed that battery twice trying to get it to turn over.. Every time i get it to turn and actually idle the idle keeps extending before dying until if finally levels and idles up.. I thought bad gas at first.. Anywho lmk if youre still on this forum.. regards..