User 6624

Just noticed this today on my 3 month old 2017 A4.

I drive with auto start stop on 90% of the time. Today in a drive thru, the car had the A/C on, so the engine never cuts off. But as I stopped in the drive thru and pressed firmly on the brake, the RPM dropped well below 1000 and felt like the engine was going to cut out. Every time I pushed the brake pedal in far, the RPM dropped to like 400 but the engine never shut off, it just felt like it was choking. The A/C was preventing the engine from shutting off, which it should, but this RPM drop should not happen.

At the same time, I lost every HD station and every FM station came in with horrible reception.

I went to work and when I left my car and got back later everything felt fine.

I use 91 rated gas and the engine was completely warmed up. Could this be a software issue?


I was updated weeks ago to 0692

HyperS4

Actually, the start/stop will still work with the AC on. It will cut out but then start the engine again when the temp sensor in the car dictates that it needs to turn back on to get the AC working again.

Your situation sounds like an issue though.

johnwc723

Alternator or break cylinder or battery issue perhaps? From my experience load on the break will put some on the engine and might knock off a few thousand RPM and then it rebounds. Could it be something with how some of your mods deal with the situation?

marklar182

Experienced similar today, with S/S ON and AC On, the car seemed to fight itself at a stop. RPM was bouncing below normal idle. Pulled the shifter into Sport while still at a stop and the idle returned to normal when S/S was then disabled.

Sounds like some bugs in the algorithm for S/S.

WesNeedsCoffee

On my B9, the engine will idle at about 800 rpm when in normal mode and 1000 rpm when the transmission is in Sport mode (engaged by pulling back on the gear selector a second time).

I've never noticed the car idle any slower than that with or without the A/C or stop/start on. Idling at 1000 rpm is noticeably smoother but it's not like 800 is anything close to what you're describing.