In neutral, no rpm drop?

[zx3zetec]

I was driving my wife's new 2008 Ford Focus today.
It is an automatic transmission.
Anyway, I thought I'd try popping it in neutral while coasting down a hill to do a little "hypermiling". To my surprise, the RPMs stayed right where they were! (1500 rmp) I tried this a couple more times during my drive and experienced the same result. The RPMs stayed the same as just taking my foot off the gas and coasting in drive.
Idle in park is 900ish RPM, so I was quite surprised...

Anyone know what's going on???
By the way, the 2008 Focus is really really nice. We got 42 mpg on a trip last week by driving 60mph with the AC running.

[fanamingo]

It's not just your car. My '99 Mercury Sable (Ford Taurus) with automatic transmission does the same thing. Even worse, when shifting from overdrive to neutral the rpms increase to what they would be if I were just in drive! I haven't hooked my ScanGauge up to see the actual effects on fuel consumption. I think it's just a characteristic of the transmission, but I don't know why it's built that way.

[achang1]

i know from the Taurus it also if you're doing a neutral coast at high speeds like 45 or higher, the RPMs will actually go up quite a bit. I believe its to have the transmission spin at the same speed the engine is so it wont destroy the transmission when you reengage Drive.

[BlackDeuceCoupe]

Originally Posted by zx3zetec

RPMs stayed right where they were! (1500 rmp)...

Idle in park is 900ish RPM, so I was quite surprised...

Anyone know what's going on???

Interesting!

My ride has a close-ratio, 5-speed tranny (S4C) with 4.4:1 final gearing.

I typically cruise @ 3000-4500 RPM (55-75 MPH).

Engine-on-coasting is 1100ish RPM, regardless of speed, 1-150 MPH...

As soon as the speedo hits '0' MPH, the idle falls to 900ish RPM too. Weird!

I *assume* this is due to some vagary in the ECU programming...

The ECU ultimately controls the idle speed in my car... probably yours too!

[zx3zetec]

Thank you all for your input!
I suppose it can all be attributed to all this drive-by-wire computer controlled stuff...
I guess it's a good thing, because once I missed neutral and threw it in reverse while going 50mph, and nothing happened :-)

[cfg83]

zx3zetec -

In my Saturn, at highway speeds, the "neutral idle" RPM is higher then my normal idle. My normal idle is between 800 and 900 RPMs. At highway speeds, the idle is usually between 1000 and 1200 RPMs. We have deduced that the ECU/PCM is changing the setting of my Idle Air Control valve because it is seeing higher MPH.

As long as your coasting-in-neutral RPM is lower than your coasting-in-gear RPM, then it's a win. But, not as good as it could be, .

CarloSW2

[ptsmith24]

The RPMs while coasting in neutral and while sitting still in neutral are basically equal. I've only tried at speeds of ~50 MPH and lower, though. I try not to re-engage Drive before completely stopping though. I do that because I am unsure of the consequences. Interesting side note: The instant MPG on the MPGuino (still calibrating, but seems pretty accurate) is about the same whether I'm coasting in D or in N (different RPMs). Fuel cut-off, maybe? I'm still not sure how cut-off works, though.

[Doofus McFancypants]

In my wife's PT Cruiser - the RPM drop VERY VERY slowly.
like over a 3 minute period they drop.
I was trying to gather data on coasting in gear compared to coasting in N and i noted the RPM did not drop.
Since i have the SG hooked up, i could see the MPG increase in both cases.

After playing with it some more - I have chalked it up to ECU Programming to try to decrease delta in engine RPM and transmission RPM.

[nascarnation]

I'm not knowledgeable about all makes, but some of this is intended to reduce the load on internal transmission parts when you go from neutral back to drive (if your vehicle speed is well above zero).

Also more engine speed to the converter means more trans pump speed means more lube flow - in some cases important to lubing various parts internal to the auto trans.

This is all made possible by the full authority powertrain electronic controls.

[Sean T.]

you guys beat me to it. I was gonna say, in my taurus, sometimes it goes up when I shift into neutral.

[Matt Herring]

I have an 05 Toyota 4runner and the rpm's drop in neutral coast compared to in drive but run higher than in drive when I'm not moving. Neutral coast is about 500 rpm's lower than in drive at 50 mph but about 200 rmp's higher than in drive when not moving.

[mopo3]

I experienced this effect when I first started hypermiling and had not known anything about the proper techniques. I thought it might have been some accessory the engine was trying to power, put unless it was the water pump I had everything else off. I wonder if there is a way to modify the the ECU to lower that idle by 100 rpm.

[93Cobra#2771]

It is a factory safety item programmed into the EEC. Keeps engine speed high enough to power all accesories, power brakes and power steering. It is typically 500-600 rpm over normal idle speed. It could be tuned out, but you run the risk of engine stall if you put a high load at low rpm. For example, if doing 50 mph , in neutral, you decide to turn hard, turn a/c on and brake at the same time.

[nascarnation]

Originally Posted by mopo3

I wonder if there is a way to modify the the ECU to lower that idle by 100 rpm.

Quite possibly if you have a brand that someone has developed aftermarket ECU tuning.
GM, Ford, and Honda for sure.

I've not found anything for the S series Saturn though.
If anybody does, I love to know.

[itjstagame]

As for idle being higher in neutral compared to in drive when no moving. This just makes sense. Granted I don't have the Fords mentioned, but the automatic is not 100% efficient and much less so when not moving and allowing that 'slip' to happen. It's not the idle that's changing, the idle is changed to handle the load when in gear. For instance in neutral you're at 1100, you switch to D and you're at 800 and you can clearly tell there's a load on the engine by the sound. It's probably the same IAC/throttle position in both cases. In P it can drop to the lowest RPM the engine will idle at because it doesn't have to worry about 0MPH in D and stalling.

[dcb]

Originally Posted by nascarnation

I've not found anything for the S series Saturn though.
If anybody does, I love to know.

Well it isn't perfect, but some s-series folks just warm up the car and turn everything on (ac/rear defroster,headlights), then unplug the idle control motor. It's manageable for the most part.

[JMags]

From what I have read the computer keeps the high rpm when shifting into neutral for emissions reasons.
The sudden change in load causes the temperature in the combustion chamber to rise and creates more NOx. This slow drop is programmed to smooth the transition and reduce this particular pollutant.

[Formula413]

I've noticed this in the van I drive at work (2008 E150 4.6L V8). If I was driving at, say, 45 mph at 1600 rpm and shift into neutral the rpms will stay right at 1600, then slowly fall as the vehicle decelerates. It's like automated rev matching. In my Escort the revs will drop to just slightly higher than idle when shifting into neutral while moving.

[93Cobra#2771]

It isn't really rev matching, just a coincidence. The EEC in your van is 11 years newer than the Escort EEC - they have learned much about engine control since then.

Nice escort, though I like my green better.

[bikin' Ed]

'06 Dadge Dakota 4spd auto. returns to normal neutral rpm if coasting at less than 35mph. Over 35, it idles about 300 rpm higher.