Quote Originally Posted by isb View Post
I think I read some time ago that the slow drop off in revs was due to emissions management - emissions are higher when the air intake is shut off quickly. If so, that might explain why the flashed cars behave differently.
Yes, usually when revs fall off slowly, its the emissions system trying to lean out the mixture. If the throttle plate is closed, injections go back to idle settings, but there is not enough air in the plenum to get to the 14.7:1 desired for complete combustion at revs. Therefore hydrocarbons spike, and HC's are a no no to the EPA. So, they keep it cracked a little to let air in, but the side effect is slower falling revs.