In neutral, no rpm drop?

[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.