Why does my 996 C4S idle higher when cold?

[Riad]

I'm trying to gain an understanding of why the car is engineered to idle higher when it's cold.

First I always warm the car until the the car comes to idle - about 700RPM, which takes about 2 or 3 min. tops. Then I keep the RPM's under 4K until the car comes up to temp, about 180 degrees. You can actually feel the tranny warm up and shifting is much easier.

After that I consider the car ready to go.

When I first start the car, and my 2001 C4 was the same, the engine runs a little rough, but as soon as it comes to idle it purrs, why would I just start the car and drive? :help:

Much appreciated!

Rob

[dr_karlb]

I'm trying to gain an understanding of why the car is engineered to idle higher when it's cold.

First I always warm the car until the the car comes to idle - about 700RPM, which takes about 2 or 3 min. tops. Then I keep the RPM's under 4K until the car comes up to temp, about 180 degrees. You can actually feel the tranny warm up and shifting is much easier.

After that I consider the car ready to go.

When I first start the car, and my 2001 C4 was the same, the engine runs a little rough, but as soon as it comes to idle it purrs, why would I just start the car and drive? :help:

Much appreciated!

Rob

Hi Rob,

You remember cars from the 70's had that Choke thingy that you would pull to start up the car. It allowed the mixture to run richer to keep tha car going while it was cold.

Newer cars from this millenium have an electronic version that does the same thing without you having to pull the lever thing.

My guess would be this mechanism operating for a few minutes until warmed up.

[Riad]

Yup, I get that. So the question would be, should you let the car come to idle (700rpm or so) before driving it?

[al123]

if you read the manual it says drive straight away, no need to wait

[Riad]

if you read the manual it says drive straight away, no need to wait

Yes. There seems to be some debate on what Porsche recommends and what may be best practice.

[Eric (Plug Guy)]

if you read the manual it says drive straight away, no need to wait

Yes. There seems to be some debate on what Porsche recommends and what may be best practice.

I start my '04 C4S Cab in the garage (it's always backed in) and exit immediately (within a couple seconds). On cold mornings, I sit outside the garage for about 30 seconds just while the garage door closes, then I take off. I am careful not to gun it while the temp is low. Once the temp is close to 180, I too can feel the short shifter ease up a bit, and I'm ready for anything.

No need to idle for minutes. Just get in and go. Just go easy the first few miles. :beer:

[Q-Ship986]

I'm trying to gain an understanding of why the car is engineered to idle higher when it's cold.

This usually has to do with emissions. My understanding is that cold (ambient temp) start is one of the most difficult hurdles in passing emissions requirements. Higher revs gets everything warmer, quicker...particularly the cats.

Point of interest: My Lexus RX avoids shifting into higher gears, and won't shift into the top gear (4th), during cold operation until the engine temp gets close to normal operating temp. In this case, "cold" means freezing temperatures. The first time I experienced this in the winter, I inquired with the dealer thinking the auto tranny wasn't properly functioning. Explanation was that it was....Lexus just wants the heater core to get up to temp more quickly--for occupant comfort.

--Brian

Edited March 23, 2006 by Q-Ship986

[RJFabCab]

I'm trying to gain an understanding of why the car is engineered to idle higher when it's cold.

This usually has to do with emissions. My understanding is that cold (ambient temp) start is one of the most difficult hurdles in passing emissions requirements. Higher revs gets everything warmer, quicker...particularly the cats.

--Brian

Ditto that. It's my understanding that the temporary higher idle helps reduce emissions on cold startup. I'm not sure of the technical mechanism, but it's probably related to what Brian said.

Cheers