matelot

Been wondering for a long time: Why cold engine revs so high ?

leeherman

Emissions.

Higher revs=faster warmup=lower emissions, therefore most modern vehicles idle higher, and rev higher in between gear changes (automatics).

Regards,

matelot

you mean to say the "instruction" to rev higher is programed in the ECU or computing component ?

leeherman

Yesiree, that's exactly what I mean.

I'm not sure if you're into the older cars like I am, but if you ever drove a carburetor equipped car, you'd remember that you had to hit the throttle once or twice before starting the car to set the choke and pump fuel into the intake manifold. The choke was necessary to richen the fuel mixture for cold starting and cold driveability. Fast idle helped warm the car quicker to get it running at its most efficient operating temperature, and the carburetor came off the fast idle cam as the choke opened.

Modern fuel injected cars like the TL don't have a choke, but they have some sort of mechanism to richen the fuel mixture on cold start. Fast idle is probably obsolete in a modern vehicle, however, it's employed to speed the warming process. You may have noticed how when you start your car from cold, it idles at around 1,500 RPM immediately, and eases up to almost 2,000 RPM within ten seconds or so. If you let the car idle, you'll see the idle speed drop way down as the engine hits its operating temperature.

Regards,

TheTriads

I second that, Leeherman's comment is very well said and explained. This thread can now be closed.

rets

Yah. "choke" was the one we had to play with in the past... I miss that old damn trick.