Unstable RPM on first start - A6 3.0T 2009

[Ivan40]

Hello everyone.

I'm happy to be part of the community, and not so happy about my first post. I have had a problem for several months with the first start. The problem is presented every time and occurs in warm/hot outside temperatures. The car (A6 2009 3.0T) idles at around 1600 RPM for about a minute. For that time the engine fluctuates and the RPM is going up and down until it idles normally at around 800 RPM. After that, the RPM is stable and never had a problem.

Any idea what can be the reason? PCV is changed. No errors logged or Check Engine lights. Actually, I don't know if that 1600 RPM is normal when starting the car (even in hot summer).

And sorry for my bad English, it's not my native language.

[MTL4]

Have you looked at your timing chain values in VAGCOM yet? What about fuel pressures? I would start there and see what you find.

[pewpewprince]

Hello everyone.

I'm happy to be part of the community, and not so happy about my first post. I have had a problem for several months with the first start. The problem is presented every time and occurs in warm/hot outside temperatures. The car (A6 2009 3.0T) idles at around 1600 RPM for about a minute. For that time the engine fluctuates and the RPM is going up and down until it idles normally at around 800 RPM. After that, the RPM is stable and never had a problem.

Any idea what can be the reason? PCV is changed. No errors logged or Check Engine lights. Actually, I don't know if that 1600 RPM is normal when starting the car (even in hot summer).

And sorry for my bad English, it's not my native language.

90% cars a6 c6 3.0t do so. especially in warm weather 20+C.

[a1dan_87]

90% cars a6 c6 3.0t do so. especially in warm weather 20+C.

I know the high idle is normal for almost any car when its first warming up. But 1600+ and unstable RPM is something I haven't heard of as normal. Not sure how the idle air control works on these cars, but a bad or sticky IAC valve could be culprit.

[MTL4]

I know the high idle is normal for almost any car when its first warming up. But 1600+ and unstable RPM is something I haven't heard of as normal. Not sure how the idle air control works on these cars, but a bad or sticky IAC valve could be culprit on first starts.

I agree, mine doesn't rev anywhere near that high on startup (hot or cold). I would have a look at VAGCOM and see if there's anything that stands out as a possible issue.

[a1dan_87]

I agree, mine doesn't rev anywhere near that high on startup (hot or cold). I would have a look at VAGCOM and see if there's anything that stands out as a possible issue.

+1. something else to note is if they're tuned. Since I went JHM stage 1, when the car starts, it often starts to 1200RPM for <2 seconds then drops to normal regardless of temperature. I'm assuming it's to help with timing chain wear or something similar with the oil/hydraulic systems in the car

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[Erick.Brenes]

Hello everyone.

I'm happy to be part of the community, and not so happy about my first post. I have had a problem for several months with the first start. The problem is presented every time and occurs in warm/hot outside temperatures. The car (A6 2009 3.0T) idles at around 1600 RPM for about a minute. For that time the engine fluctuates and the RPM is going up and down until it idles normally at around 800 RPM. After that, the RPM is stable and never had a problem.

Any idea what can be the reason? PCV is changed. No errors logged or Check Engine lights. Actually, I don't know if that 1600 RPM is normal when starting the car (even in hot summer).

And sorry for my bad English, it's not my native language.

You have a problem with the SAI (Secondary Air Inyection), clogged or dirty pipes could be the cause. I don't know how to clean it, I heard some people saying you can do it yourself and other people saying it needs a specific tool.

I bet you don't get this problem when starting the car after it reaches operational temp.

To be sure that its SAI:
1. does this issue appear only when the engine is cold?
2. if the car is cold, you start it, and you put it in Neutral (this stops the SAI operation)... Do you see the same behavior or does it go away?

other things to consider is injectors. As a rule of thumb, if the failure goes away when hot, is a mechanical failure.
You need to go on the live data part of your ODBII and check the block 14, line 2 or 3 is the amount of missfires. If you see a value above 1 when the Revs fluctuate go to the next blocks 15 and 16.
In the block 15 you will see misfires in cyl 1-3 and 16 cyl 4-6.

other channels that may be useful in live data mode are 77 or 78 (I don't remember) its the SAI live data, mainly the 4th line where its says if its ok or if its in abort.

I know there is another channel around 100-112 where you can see the voltage of the 6 injectors.

Also check 93 for tensioner deviation, both sides. The value has to be between -8°KW and 8°KW. I would start saving money for the full kit (about 1.3k usd) if I had it at 6°KW.