2008 3.6 Q7 Engine - Loud, Rough Cold Start
 

Just picked up a 2008 Q7, build date 11/07. When the engine is started cold, the engine noise is a rough and loud for 20 seconds and then quiets down to a normal smooth sound. (The manual does makes mention of loud noise at start). I don't get any oil pressure warnings or anything related to prior oil pressure issues that should have been well resolved before this vehicle was even built.

There are mild RPM flucuations at start as well.

Don't see this phenomenon on my 328xi.

Do others see this with their Q7's?

Thanks.

I've noticed that after 20 or so seconds after start up...
 

it sounds quiter...never thought much of it though.

sounds similar to the oil pressure issues

Re: 2008 3.6 Q7 Engine - Loud, Rough Cold Start
 

It does sound similar to oil pressure issues but there are no warning lights and the sounds improves fairly quickly.

This is a 2008, shouldn't have the oil pressure issue.

Same thing with our 2007, but thought nothing of it. Normally
 

I've seen Subarus rev higher at the beginning because it helps the coolant get up to the normal operating temp quicker. The engine noise on the 3.6 is rough for like 10 seconds, but it goes away. Haven't really thought of it though.

Same here. It idles between 1200-1300 rpm for first 30 seconds then
 

settles back down to around 800 rpm. If I drive off while the rpm's are still high then it's a little jerky until it gets warmed up. I live in Hawaii so it's not a "cold" factor but just the fact that the engine has been idle for several hours. If it sits for more than 6 hours it will do this but if it's only been a couple of hours then it starts smooth and is ready to go right away.

We also have a 2005 TT with the 3.2L V-6 engine and it has always done the exact same thing so I didn't think anything of it in the Q7.

Like you, my BMW 535i doesn't do this either. I just look at it as a "quirk" of the 3.6 Q7. I was also raised to believe that you should let any car warm up for a little while before taking off so I'm in the habit of starting the car immediately upon entering then while it's warming up I put on my seat belt, set the stereo, etc.

"runs in the family"... my 07 3.6 Touareg does the same.

Ours is exactly the same(3/07 build date)
 

I was afraid of the oil pressure issue and had the TSB done, but it still starts as you describe when cold. It is quite disconcerting to me. Smokes quite a bit as well. My 02 Boxster would occasionally smoke upon cold start but no increased noise level. The 3.6 sounds like a diesel as it starts. Ours also makes a racket around 6K on up rpm on hard acceleration. I was told it is the direct injection when I had a serviceman ride with me to hear it. I did not hear the same noise on an 08 loaner Q7 3.6 I drove, so who knows. I figure the whole thing is warrantied while I lease the car so if it blows up I get a new motor for free...

It's the secondary air injection pump....
 

Listen closely near the intake. It will turn off after about 30 seconds after a cold start. It's purpose is to inject fresh air into the exhaust gases on a cold start to reduce emissions (CO and HC). Most of the noise at startup that you hear is this and not from the engine itself

The 2.5L 5 cylinder VW engine in the MKV Jetta and Rabbit do the same thing