C5 S6 - Warm starting issue (MAF, O2, etc..?)

[Brooklyn67]

About 9-10 months ago, my S6 was having a warm engine starting problem, seemingly in warm weather. After the engine/car was shut down after driving for a while (standard operating temperature), if the car "cooled" for a bit, but the engine was still warm, starting was very difficult and it felt like a "rich" condition as the engine was trying to rev when it fired and I needed to modulate the gas pedal to get the revs up and then finally even out. It seemed like a MAF issue and my shop's OBD sensor confirmed the engine code. I replaced it and the issue cleared up.

Less than 5K miles later, the issue is back - warm engine hard starting (no issues with cold starting or hot starting as before). The other day, when it got to 60degrees in the NE area, the engine didn't even start when "warm" and I smelled gas. I have not rechecked what engine error codes may be at fault yet or touched anything yet. I just wanted to get some opinions first. I have a hard time believing that the MAF is at fault again, but I guess anything is possible. Perhaps O2 sensor? Maybe even a very dirty K&N air filter (which I'll check today)?

Thanks.

[brokenwrench]

Sounds like a weak ignition to me. I'm not as familiar with the 4.2, but have you checked the ignition module(s), coils, plugs? Do you have any codes showing up?

A dirty MAF sensor might be the issue, more than a dirty air filter. Which brand of MAF sensor did you put back in there (I'm not sure if the 4.2 is as sensitive about MAF brands as the 2.7, but something to check)?

But if you're smelling raw fuel then it's because it's not igniting. Even if you had restricted airflow and good spark, you wouldn't smell it. It's either running way too rich (less likely) or not igniting (more likely).

[Brooklyn67]

Thanks brokenwrench.
I bought the MAF from ECS. I just spoke to their tech dept and he mentioned that sometimes the oil in a K&N filter can come through the intake and coat the MAF. Though I've used K&N for years on many old bikes and cars, I didn't think of connecting the 2, which may be the issue. I'm going to buy some MAF cleaner today and a spare paper air filter to see if I can clean and solve this issue. I'll have an update soon.

[JMURiz]

Have you tried turning the key to the 'on' position for a second before cranking it over? I had that issue in the heat of the summer and this corrected it.

Granted it may have been something else, as I've had a lot of maintenance done that may have fixed it (not 'in time' when the timing belt was serviced etc)...but I still do it out of habit.

[kino]

I had issues when warm because of a crank shaft sensor. Car would start cold but if I stopped and tried to restart it wouldn’t. Couldn’t tell if that’s what you are experiencing?


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[Brooklyn67]

The warm-starting issue specifically happens only when the engine is shut off (when hot), allowed to cool for a short time, but not so that it's cold. For example, I drove to the Auto Zone yesterday (50 degrees outside) and it was a 15-20min drive. Car started fine when cold, ran fine during the drive and then I got to AZ and shut it off. The S6 sat for 20-25min, while I got stuff to clean the MAF and they offered a free OBD code reading. The codes that were spit out were:

P1296 - Cooling System Malfunction
P0441 Evaporative Emissions Systems Incorrect Purge Flow (existing code failure since I bought the car 3-4 years ago - previous owner said it was gas cap related and never fixed it...obviously, I haven't fixed it either)

When I went to start the car, it kept on cranking...stuttered a few times...cranked more, but no start. I let it sit for 5min and then tried starting it again - cranking stuttering and trying to start (as mentioned, the condition seemed like it was either flooded or too rich a mixture - almost like the ECU thinks that the car is cold). It finally started a bit and I needed to modulate the gas pedal to bring up the low revs without stalling it and then it (felt like) the excess fuel cleared the system and it revved up fine. I revved the engine to 2-3k a few times (engine felt strong) and then it settled into a steady idle. This has now happened to me a few times as well as it happening to the engine in the same way about 9-10months ago before I replaced the MAF. It kind of felt like when my old bikes or old BMW (2002) was flooded (carburated engines) and getting it to start by opening the throttle wide open or pressing the gas pedal down in the 2002 and cranking the engine.

I got back to my parking lot, removed and cleaned the MAF and replaced the K&N filter with a new paper one. Once the MAF was dry, I put everything back together - the engine was still warm - I went to start the car and the same issue persisted. So it seems like this didn't resolve the issue. Could it be an issue with the purge valve and error code P0441?

[kRussia]

Replace the coolant temperature sensor, If they go it won't start when it's warmed up.

[Brooklyn67]

Thank you kRussia - that makes sense as well in regards to the warm starting issue.

Reet

[chris86vw]

yes good call kRussia especially since when they fail they often don't throw codes as the temp they are sending is still plausible so at first glance they seem fine.

Can't hurt to check the measuring block to see what its reading the next time you have the problem. I remember this all the time when I Was at VW/Audi and these and similar engines were having problems with bad batches of sensors from the factory, totally warmed up car reading a negative temperature but no fault.

[kRussia]

Your welcome hope it helps. Side note; what part of Brooklyn are you from ? Grew up in Sheepshead Bay my self. Kind of miss it from time to time.

[AudiNike12]

Yeah, def sounds like the coolant temp sensor. Had the exact same problem myself 6 months ago when I bought the car. Started fine when cold but not when warm(after waiting a little while). Sometimes it did. Although I got a code on the temp sensor, so it was easy to spot for me. It was actually doing that when I went and looked at the car but I thought it was no big deal and would fix it myself. The car was very cheap so I had to buy it

[Brooklyn67]

I grew up in Flatbush and Brooklyn Heights and I currently live in the more-and-more-gentrified area of Bedstuy (a hood that I would have never gone under, over or around when I was growing up - it was a war zone).

I love Sheepshead Bay - I used to go fishing there when I was a little kid.

[kRussia]

miss it

[02 A6 2.7T]

The warm-starting issue specifically happens only when the engine is shut off (when hot), allowed to cool for a short time, but not so that it's cold. For example, I drove to the Auto Zone yesterday (50 degrees outside) and it was a 15-20min drive. Car started fine when cold, ran fine during the drive and then I got to AZ and shut it off. The S6 sat for 20-25min, while I got stuff to clean the MAF and they offered a free OBD code reading. The codes that were spit out were:

P1296 - Cooling System Malfunction
P0441 Evaporative Emissions Systems Incorrect Purge Flow (existing code failure since I bought the car 3-4 years ago - previous owner said it was gas cap related and never fixed it...obviously, I haven't fixed it either)

Could it be an issue with the purge valve and error code P0441?

I had the same issue with the P0441 code and warm start issues ... replacement purge valve fixed it ...

$25 here :[/I] https://www.amazon.com/Bosch-0280142...ype=automotive

[Brooklyn67]

Update:
I replaced the Coolant Temp Sensor and the Purge valve - the error codes were also reset.

After a few days and driving about 200-250 miles - the warm starting issue seems to be resolved.
In addition, the check engine light has not come back on. The S6 also "feels" like it has more power and the engine is a little more responsive. I would assume that this is due to the ECU feeding in the correct air/fuel mixture (ie. Coolant Temp Sensor replacement)...previously, it felt like it was running very rich.

One side note: For anyone who buys their new Coolant Temp Sensor from an auto parts store (ie. Auto Zone), make sure it comes with a new C-Clip. The C-Clip is surprisingly fragile, especially if the old one has been on the block for years. The C-Clip broke broke when I was removing it (the sensor was difficult to remove as well). I realized after-the-fact that my CTS didn't have a new clip included.

Thanks for everyone's help/suggestions - especially kRussia.
65+ degrees today in the northeast - wish Audi was a convertible!

[kRussia]

glad it worked out

[duanus]

I had the same issue with the P0441 code and warm start issues ... replacement purge valve fixed it ...

$25 here :[/I] https://www.amazon.com/Bosch-0280142...ype=automotive

Thanks for the information. I used the link and bought the valve after making sure it fit my car. No CEL!