This morning it was below freezing, and I started up my A4 so I could run the defroster while scraping the frost off the windows (ugh).

Normally when the engine is cold, it idles around 1100-1200 RPM on startup and then it drops to 750-800 after a minute or so. This morning when I started it, it went straight to the slower (750-800 RPM) idle. Is this a problem, or is it normal for sub-freezing starts? I would think it would need the fast idle more when it's colder out.

I did a search, and found this thread where someone with a B7 had a similar observation: https://www.audiforums.com/m_176725/tm.htm

but no answer.

 

its not a problem at all the system is working rather well which is rare

 

So it's *not* supposed to fast idle in sub-freezing temperatures? I've never heard of that before. [&:]

 

Mebbe your oil froze in the heads. j/k

 

I wouldn't see it being a problem. I rather like it when mine starts sometimes and goes right to the slow idle.

 

I have noticed this as well, last winter. I was surprised to see that on a cold start it was right at 800-1000 rpms. But sometimes and more often like the past few days, 35ish degrees in the morning, it goes to about 1200 rpms and then settles down to normal idle very quickly. I wonder what it all depends on??

 

older systems had a manual choke for cold start, newer are electronic and a pain in most cases its the throttle body and need cleaning due to carbon build up

 

Well, the idea behind the fast idle is to warm up the catalytic converter more quickly to reduce emissions. Once the cat reaches operating temperature, the idle speed drops to normal (~800 RPM on a 1.8T).

I was just surprised to see the fast idle not happen on a colder morning. Every other car I've owned has done the fast idle even in sub zero temperatures.

I doubt it is the throttle body sticking, since the car started fine and responded to the gas pedal fine. It just didn't do the fast idle for a minute or so on startup.

 

My car does the same thing and it is only when the temp is at or below 35. I was told its not a problem. The only theory i can come up with is since its really cold the motor needs to be brought up to temp slower to prevent damage to parts. And oil is thicker which will circulate slower.

 

No, the 02 sensors have a feature where they heat up on their own for that. I dont know about B6's, but there is also a secondary air injection pump for that purpose as well as far as start up emisions go.