Quote:
Originally Posted by Daox
IMO with modern fuel injection this is not a big issue. High idle is more about getting the CAT up to temp than it is about idling nice.
If you are running a carburetor it is more of an issue.
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Most cars also retard ignition timing for a while to get the catalyst up to temperate. All this does is start the burn late, so that it's still burning when the exhaust valves open. Some of the combustion that would have pushed on the pistons goes out the exhaust and heats the catalyst.
Disabling cold ignition retard help cold start fuel economy but gets rid of acceleration of cat heat up.