Cold Wx lower idle in drive
 

In cold weather, my Matrix automatic idles higher in (N)eutral than in (D)rive.

Is it more economical to idle, while briefly stopped, with the car in gear in this case?

Thanks.

The reason it idles higher is that it is released from the drag of the gearbox.
The ICU makes it use just enough fuel to enable combustion, which makes it rev a bit higher than it does under load, where the same amount of fuel is not enough to overcome the drag so the ICU adds fuel to prevent it from sinking below the minimal RPM.
Despite the higher revs, it will use less fuel idling in neutral than it does in drive.

My cars idle consumption in neutral is about 60% of what it is in drive, by the gallon per hour readout on my UltraGauge. It idles a bit higher.

Which is one of the many reasons for Scangauge/Ultragauge/Torque - to answer this type of question for your particular vehicle.

Regarding scan gauges or other information devices. Do you have any recommendations in terms of brands or models? I have a 2004 Matrix XR automatic, FWD. Thank you.

All three should work well with your car.

If you have a smart phone, the Torque app works well and is cheapest. You'll need a Bluetooth OBDII adapter.

Ultragauge is inexpensive and works great. This is my preferred option as I like having a stand-alone device for the car.

Scangauge has some additional features over the Ultragauge, but you pay for them. The SGII is about twice the price. The SG-E is a happy medium. You can support the site by buying a Scangauge:
EcoModder Store: Get Stuff, Support EcoModder - EcoModder.com

(You're welcome Darin!)

SG-II is overkill in my opinion unless you have a hybrid or other car that can use Xgauges. SG-E is so gimped you might as well save some money and go with the UG.

UG is my prefered daily use device, but the SG-II is a great diagnostics tool for hybrids.

I've used both in the Corolla & prefer the Ultragauge. It fit's nicely above the steering column w/o really blocking gauges. Not sure if your Matrix has a similar cluster?

Also like the adjustable alarms of the Ultragauge & the ability to better fine tune the MPG calibration. The Scangauge needs to run through a few tanks to dial in the calibration where the UG will let you fine tune after 50 miles into a tank.