Idle

[rh77]

Originally Posted by Compaq888

no, it goes up for a second then comes down to the same rpm as it was in D. Here is how i think it works...I think Bunger will agree with me.

I stop, put in N. Rpms go up because there is less load for the same fuel input then computer realizes there is no load and lowers rpm in neutral to the same rpm as it was in Drive. When I put the car back in Drive the rpms dip to 500rpm because of the Torque converter and the engine adds more fuel to keep it at 650rpm. Both N and D are 650rpm. But the difference is N has no load so the engine uses less fuel to idle. In D the engine idles in same rpm but uses more fuel because the Torque converter is now working.

I don't have a Scangauge, I use mpg trips to see the changes in my gas mileage and this website to see what works and what doesn't work. I think so far my street mpg is 23-24mpg. While my freeway should be around 35mpg. Every month I do something new to the car which improves my mpg.

Actually, I figured it out randomly one day waiting in the car when it was running. If I moved the shift lever ever so slightly between N and D, the engine would tach-up anticipating the need for more RPMs to sustain the need of the transmission's resistance. If I put it back into N, then it would tach back down to idle.

I've learned a few things from this thread, I think. For idle, it would take less fuel. But for coasting: I have always read that putting an automatic in N to coast doesn't save mileage because of a loss of vaccum or some sort, and that essentially you're not using any fuel at closed throttle until you reach a certain RPM. Wouldn't it take more fuel to keep an engine idling instead of coasting? Also, what part of the transmission will wear out becuase of placing the vehicle in N, then clunking it into D while stopped? ...mine sometimes is a pretty hard engagement in the Integra, even warmed up.

I'll give it a try and see what happens, but from a cold start, I leave the transmission in gear to heat it up quicker (is this correct?) I used to flip up to N to let it idle higher to warm up the engine faster (like waiting at a light on a very cold day, or at the airport parking lot ticket payment booth line).

I agree with Matt -- automatics are some kind of witchcraft -- I've said it before, but I have no clue what the heck goes on in there.

RH77

[rh77]

Darn double post -- when will they perfect WIFI??? (Dammit)

Anyways, I forgot to mention that D-to-N basically is the engine's unexpected reduced load, then it figures it out and back to idle we go -- manuals won't tend to do it because of the lack of a TC. I miss my manual...

RH77

[diamondlarry]

I stop, put in N. Rpms go up because there is less load for the same fuel input then computer realizes there is no load and lowers rpm in neutral to the same rpm as it was in Drive. When I put the car back in Drive the rpms dip to 500rpm because of the Torque converter and the engine adds more fuel to keep it at 650rpm. Both N and D are 650rpm. But the difference is N has no load so the engine uses less fuel to idle. In D the engine idles in same rpm but uses more fuel because the Torque converter is now working.

I think this sounds right. I've seen some cars that the idle control is so smooth that you hardly notice a change in rpm's when shifting in and out of gear. It seems like my Durango was that way; I think.

[Compaq888]

Originally Posted by rh77

Actually, I figured it out randomly one day waiting in the car when it was running. If I moved the shift lever ever so slightly between N and D, the engine would tach-up anticipating the need for more RPMs to sustain the need of the transmission's resistance. If I put it back into N, then it would tach back down to idle.

I've learned a few things from this thread, I think. For idle, it would take less fuel. But for coasting: I have always read that putting an automatic in N to coast doesn't save mileage because of a loss of vaccum or some sort, and that essentially you're not using any fuel at closed throttle until you reach a certain RPM. Wouldn't it take more fuel to keep an engine idling instead of coasting? Also, what part of the transmission will wear out becuase of placing the vehicle in N, then clunking it into D while stopped? ...mine sometimes is a pretty hard engagement in the Integra, even warmed up.

I'll give it a try and see what happens, but from a cold start, I leave the transmission in gear to heat it up quicker (is this correct?) I used to flip up to N to let it idle higher to warm up the engine faster (like waiting at a light on a very cold day, or at the airport parking lot ticket payment booth line).

I agree with Matt -- automatics are some kind of witchcraft -- I've said it before, but I have no clue what the heck goes on in there.

RH77

Yeah when the car is cold there is no point in flipping back and forth through N-D. Also the parts are stiffer when they are cold. When the engine is up to temp it's the best time to do it. Doing this will wear out the Transmission cable and the motor mounts. It should give a boost of 1 solid mpg if you do it the entire tank.