Rough idle

[mjennings23]

I have a feeling I already understand this but figured it worth getting some unbiased opinions from you fine knowledgeable folk!

Engine is an M54 3.0

I sometimes get a rough idle on a cold start, with the following symptoms/parameters;

• Only happens when the engine is cold
  Only happens when the car hasn't been driven for at least 10 days
  Disappears after around 10 seconds and drives fine after
  Won't repeat again until car left unused for time stated above

My first instinct was bad coils, but that isn't something that fixes itself predictably after a few seconds. The car drives and accelerates fine under full throttle and high RPM when the coils are worked the hardest.

So, problem solvers! What do we think it could be?

 

[Jfgoldfish]

Sounds like you've found the solution; drive it more often :wink:

If its just a slight roughness I wouldn't worry. It probably is just because it has been sat unused.

 

[mjennings23]

Well, from what I understand it's quite common, especially with the heat and humidity lately, that moisture ends up getting to the coil packs. This is what causes the issues, but naturally once the engine fires up it evaporates off moisture quickly hence it is settling down after a few seconds.