Coasting vs Lean Burn
 

I purchased a 1998 Civic HX about a month ago, recently hooked up a ScanGauge II, and I've been averaging around 53 mpg. My commute has a couple steep long hills and I'm wondering if it's better, for FE (Fuel Efficiency), if I stay in lean burn mode or put the car in nuetral and coast down the hill.

Honestly, your ScanGauge can answer that better than we can. Does it go into lean burn when you go down hill? Your car actually should go into Direct Fuel Cut-off, literally cutting off the fuel when you are not using your accelerator--and other unquantifiable conditions. My Ultragauge shows that my engine barely uses more fuel coasting in gear than in neutral. There is a debate between coasting in gear and in neutral. You can coast further in neutral and get really good mileage, but if your car goes into DFCO, you would be able to coast a shorter distance without using any gas at all.