propellerhead said:Good question. Too bad no one has answered it yet. I'd like to know too.
mrvax said:An automatic transmission has no load on the engine in neutral so the idle speed will be highest. When you put the car in Drive, there is a small load on the engine so the idle will come down some. It is normal.
Red03Mustang said:I understand what you're saying, but what I mean is, the car is actually programmed to run fewer RPMs in "D" than in "N". That's the part I don't get.
I can program both "D" and "N" to 800 RPM, and it'll stay there, no matter which one I'm in.
I'm just wondering if there is a reason the car is programmed to hold a lower RPM in "D" than in "P" or "N". It's not the engine load if the car is specifically programmed at a certain number RPM, and I'm just wondering WHY it is programmed lower in "D" than "N" from the factory, instead of just a steady RPM accross the board.
I hope that makes sense.
03ghoststang said:Even though the rpms are controlled by the computer there is still a mechanical load being put on the enigine by the tranny. So when its engaged in gear "D" the car is ready to go just release the brake pedal and it will take off slowly. So i still say the load factor is to why the rpms drop...Like when you turn on the A/C the computer adjust the rpm but when you take off you can feel the load being put on the engine by the A/C compressor. So its similar to the tranny dropping the rpm's to 560 because its a bigger load being put on it, but if the idle speed in "D" was 760 the car would have a tendacy to wanna roll more.. Try doing a stall speed to that rpm see if the car would want to roll more even though the brakes are applied..
... and the computer adjusts it back to the programmed idle speed.Red03Mustang said:I know if you put a car in "D" it puts load on it and makes the RPMs drop.
I'm still not buying the idea that Ford set the P/N and D idle speeds to mimmick what the old carbureted engines did.Red03Mustang said:I think, and what another poster mentioned sounds right, is that because of the MECHANICAL drop in RPMs that would naturally occur from going from "N" to "D", the computer is set at approximately the RPM it would naturally drop, and therefore tries to even out the RPM within the range it "thinks" it would drop to.
You're welcome. I thought you stated it pretty clear in your first post.Red03Mustang said:Properllerhead, thanks for understanding my point.
Red03Mustang said:Now, haha... what makes them set Neutral at a higher RPM than Drive? Doesn't THAT just waste gas? Or is there something I'm missing about how the gears engage? Do they NEED a higher Neutral RPM so that it "falls" into place when the tranny engages?
jstreet0204 said:The same idle in nuetral would stall.
Red03Mustang said:Well, I don't know about that, because I can lower the neutral RPM to 500, and it won't stall. I've experimented with lower and higher RPMs, so I know how the car acts in these ranges.
The reason I'm messing with it at all is because the car occasionally acts like it wants to die right after the initial RPM burst, when the needle's dropping back down. It'll fall all the way to about 400 RPM, kinda blurb a sec, then kick up to 600-700 RPM range where it is programmed to be. Kind of hunting for the idle, I guess. I'm not really sure why it does that, so I thought maybe adjusting the RPM idle/drive would help. It only seems to if I up it to around 800 for both.
I was just wondering mainly if there is any reason that I would need to keep the span that the computer has programmed in there. For example, since it has approximately a 200 RPM difference between neutral and drive, is I up the Drive RPM 300 RPM, should I make sure the Neutral RPM is 200 higher than it sill, or can I set them evenly?
That's just my curiousity. It's not that important I guess, but I was just wondering if anyone on here had experimented with it and possibly had an answer.
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