I recently purchased a new 2013 Audi A4 quattro (manual) about a month ago and started having an issue with an erratic idle. I have about 1500 miles currently on car.

Running the car in stop and go traffic (without running air conditioning), I have occasionally noticed that whenever the car is rev'ed up past 1500 RPM and come to a stop the RPM would drop to around 600-700 RPM and car would shudder/erratic idle (similar to running out of gas) but never stalls. At cruising speeds the car would run fine and the MPG is running around 28/24 highway/city respectively. Funny thing is that when I have the air conditioning on I do not notice this issue. Running the air conditioning at idle is around 700-800 (without 600-700).

I do live in Florida where it is mandatory that gas has no more than 10% ethanol alcohol.

I took the car to Audi deal last Friday where they suggested that I may have bad gas in car after mentioning that I usually filled up at Racetrack. They suggested that I should ONLY be using 'Top Tier' gas stations like Chevon, Mobile, Shell.

After getting my car back these are the comments from the tech.
-------------------------------------------------------
The RPM seems to drop low
Caused by
Run GFF no faults. Sample Fuel Quality, Fuel does not smell correct. Tested fuel for alcohol content was 11%, Tested fuel on Audi premisses it is at 7%. Unable to test for water. Filler neck is B locked, Removed fuel from tank, replaced fuel with fresh fuel.

Car would shudder occasionally at idle and idle would drop. Replaced fuel. Let idle and now car is operating as designed. Shop foreman verified concern and repair.
--------------------------------------------------------

So they drained the fuel tank and added new fuel which they "claim" solved the issue.

It sounds like from the Tech comments that no error codes were present and could not verify that water may be present in gas.

After left dealer, filled up rest of tank with Chevron 93 octane and also added an extra bottle of Techron to see if this would help.

I was driving car today and still noticed problem is still there. I am going to burn off the remaining fuel and hope this problem clear up but I am not so optimistic.

Could anyone provide any ideas or suggestions to my Audi dealer for help troubleshooting this issue?

Not sure where to go from here.

 

Make note of exactly when it happens... temperature outside, how long has the car been running, engine temp, etc.
Unfortunately, to get this corrected, you may have to complain and duplicate it. Take video when it happens.

 

Thanks for the tip ...