So I took off the resonator and wanted to hear the hemi. It revs up fairly quick but when u let off it idles down really slow. My question is why and how they (dodge) did this? Does it give less engine braking? Is that why our 390hp motors get more mpg than previous hemi trucks?

 

The idle is slow because it does not need to be any higher.

We get better mileage because of VVT/VCT and the MDS.

 

I know the truck has an extremely low idle speed, but what causes it to return to the idle speed sooo slowly?

 

Why does it matter why we get better MPG, its just a good thing.

 

Oops, I misread. Is the engine warm when you are revving it?

 

About the engine braking....If you are running in tow mode, I've noticed that it downshifts for you when you slow while driving and hauling. Thought it was nice to have while slowing down on hills and to stops...

 

Idle...welcome to throttle by wire.
Step on the gas pedal and send a signal to the ECU.
ECU decides its best to idle down slow because of....whatever...

Also in play is the tranny. You have a slipping type of torque conveter.

and call it what you want, you know what I am talking about when I type ECU...
PCM
ECM

Engine control unit or module, or power control module

 

ECU is the best term

 

My 4.7 does this also. Rev it and it idles down slow. I would guess engine management on this. I have owned other drive by wire vehicles and they did not rev like this. My Subaru Forester was similar to this but I read that it was programmed that way to keep the rpm's up when shifting gears. Mine was a manual. I don't see where this idea would fit in with the Ram.

 

The PCM is actually what controls the motor. PCM = Powertrain Control Module