S6 misfires when cold

A6 All/ S6 All
#1

Hello Forum.

I am new on this site so please be gentle :slight_smile:

I have an S6 from Oct. 2006 with 233.000 km. I have had it for 2 years now.
Idle at cold starts are rough for the first 60-90 seconds.
When 10 deg. outside temperature it starts OK with rough idle for the first 60-90 seconds.
When 0 deg. outside temperature it is very rough idle, “almost misfires” for the first 60-90 seconds.
When -5 deg. outside temperature it misfires on randomly cylinders for the first 60-90 seconds. If I give it a little throttle and hold it at 18-2000 rpm there is no misfire but rough high idle.
As soon as the 60-90 seconds are gone and the idle drops to the normal 640ish rpm the car runs smooth.
If I use the parking heater and heat the car before start, the idle is smooth, even at freezing temperatures.

If I understand it correct, the first 60-90 seconds are some kind of “catalytic converters fast heat up programme” ?

VCDS shows no errors, except for random misfires at freezing temperatures if I do not hold my foot light on the throttle.

Recently I had an injector that failed so all 10 injectors are now new, also the sparkplugs and coils are new. Same as fuel and air filter.

Shortly after I got the car, the engine got a renovated block, as cylinder 5 and 10 was scored and made metallic knocking noise. I knew about this problem before purchasing the car.
Idle at cold was rough before and also after engine renovating.

A year ago (20.000 km) a new intake manifold was installed and also a carbon cleaning was done.

The rough idle at cold is not new, it has done that since the day I got the car. What new is that for the first time since I got it, there has been temperatures here in Denmark below -5 deg.

After the 60-90 seconds when cold, or when hot, it runs smooth.

Long Term Fueltrim reads +/- 1 % on all four banks.

Any idea where to look.

#2

These cars and also new BMWs run very poorly at cold start. Very late ignition and injection timing to heat the catalysts up as fast as possible. It is normal

#3

My car even with the JHM Tune, just does not like sub zero C starts.

Typically runs rough for the first 5 mins and then it’s fine.

I’ve found what I do is let it idle for 2 mins, and shut the car off and restart. Usually does the trick for me.

#4

Is it tuned?

What fuel are you putting in it?

#5

Welcome pipedane. Ask all the questions you like. This forum isn’t like other forums. We are all here to help and support eachother.

What your getting is the SAI cold start warm up. The colder it is the more aggressive the SAI (secondary Air Injection) system is. So the colder it is the more likely you are to misfire. Over all its the cold start scheme and its overly aggressive. The biggest issues people worry about is the misfires as your car is missfireing and that is not only bad for the motor is can lead over time to destroying the cat.

The JHM tune helps get your car though cold start with less fuss. You can remove your SAI system and opt for the JHM tune with the SAI delete that will help further… The JHM tune also makes a ton more power but that is just one side of the tune. The cold start and other supporting parts make it a good investment.

Like you said. Parking in a garage will keep the car in most cases from cold starting. Over all you want some sort of cold start feature to help get the car warmed up quickly as its good for the motor and other hardware. But the cold start how Audi has it set is a bit aggressive

#6

Cold starts and SAI sucks. I have seen this issue in the past, even on tuned cars it can stumble first 60-90 seconds. I’ve heard this even happen with SAI removed. The first 60-90 seconds can be annoying for sure.

As Justin noted misfires are bad for the engine and cats, but honestly there is no great solution but the above helps. It’s not good to idle these cars or just warm them up in the driveway before driving. However on the flip side you don’t want to just start it up and punch it, really all you can do is get in and drive smoothly Low revs and in a few minutes you’ll be fine. By that time you will be at good operating temps as well.

#7

I started driving the long way out of my subdivision for this reason. Low speed, low rpm. That way by the time I hit the open roads its all warmed up. Simple, but seems to work.

#8

Treat em like a race car. Little idle warm up, then low load driving till closer to operating temp :smiley:

#9

Race car FTW. that’s the way to do it.

Seriously tho. If you can start the car and put it into R quick enough sometimes you can trick the SAI and it won’t kick on. Also remember even your owners manual says DO NOT LET THE CAR SIT AND IDLE WHEN COLD. Start and drive within 5 seconds.

So the start and drive slow low safe under 2500rpm for the first few is the best way to go.

#10

Thank you all for chiming in.

This rough idle has been bugging me for month now!

Many thing has been considered and inspected, SAI pump valves and piping, vacuum leaks, coolant temperature, air temperature, mass airflow, fuel pressure, system voltage. The spark plugs, injectors, ignition coils and intake manifold are new, and the carbon cleaning is somewhat still fresh.

Why didn’t I ask this forum before?
It is not better nor worse now. Only it did get me worried that that the car would run even more rough when we saw freezing temperatures earlier this year. But after reading of yours experience with the s6´s rough idle, that “its by design”, that took some load off my chest.

I am really happy with “My” S6
It is a company paid car, which I may use as my own. The company pays all expenses, parts, gas, insurance, road tax, every thing. But as a gearhead I do the wrenching myself.
My boss (who pays for the S6) is also a gearhead, but he is not wrenching.

#11

Yes we are all hear for eachother. Ask anything. Seriously…

The S6 can be a real monster and while there is only one shop to get performance parts from. It happens to be a really good shop. All of the JHM products are impressive and they all help not only the car run better but faster…

depending on where you live the cold starts should start to fade away over the next few weeks as the temps rise.

#12

Company paid S6? I need that job lol! ;D

#13

Yes; do this! As this is how I always start up my car in summer or winter!