The drop in RPM on startup is likely due to O2 sensors that run at a default setting until they heat up to operating temp, at which time they feed real info to the computer and then your RMPs drop. I see no reason not to at least give this amount of time to the engine to allow the oil to circulate before I put it under load. I have 229k miles on my '99 F150, because I baby it.
On increasing mileage, an intake helps for about 2mpg. I add 100% acetone to each tank of gas, at a ratio of 3 ounces acetone to 10 gallons of gas. This has consistently gotten me a 10% increase in MPG in other vehicles. I've already started doing it in my new 05 Lincoln LS. Can't say if the trend continues in this car yet. I need some more testing over time to be sure. But I know in my truck that gauge falls so much quicker every time I forget or run out of acetone.
I got that acetone idea from a site about high mileage driving. It's one of many tricks they use. They also talk about finding non-ethanol-added gas. I don't think this option exists anymore. All gas has that alcohol in it drops your MPG. The acetone works because it breaks up the surface tension of the gas molecule, allowing it to atomize in the engine better. People fear it will impact their fuel hoses. I've never had a problem. Point is, gas is a solvent and so is acetone. If gas can go through a fuel line and not disintegrate it, then so can acetone. There are something like 300 additives in gasoline and one of them is acetone. So don't discount it out of hand before you try it.
I use a glass measuring cup with ounce markers and a funnel. Each time I fill up I add, for this car, about 5 ounces of acetone. It's better than adding Techron, as far as results and cleaning ability, and far cheaper. I buy acetone by the gallon at Home Depot for about $16.
What those high mileage guys would do is, after getting the best gas they could and adding acetone, they would extra seats out of the car, every possible piece of extra weight. These guys would take the spare tire out! Then they would form homemade wheel well covers, like on the back of one of those Honda Insights:
That's the destination of the high milers. Pulling off any external drag items like wind deflectors, railing/storage bars, and then making those wheel well covers. If they could get another mpg to brag about, they would take out their driver's seat and replace it with a lawn chair.
But what you have to realize is that gas, even when prices are high, is probably the smallest or next to smallest cost of ownership. If the car is paid off and you only have liability, maybe gas is more expensive than insurance. But are you financing? That's more than gas. Do you have expensive repairs? That's more, too. I already spent a lot on my car in maintenance and I've had it a couple of weeks.
So enjoy this big, luxurious car. Stomp on that gas pedal occasionally. If you start feeling guilty about your MPG, then just keep your speed down, keep your foot out of it. That's really the main thing, they say. You can conserve the most just by slowing down and reducing the air resistance.
