It's pretty unlikely that weight reduction will help your car. Big, torquey, tall-geared American cars generally don't produce any results from weight reduction. If it would help, it would have to be a lot; your car probably weighs 3500 lbs or more; taking 100 pounds out will never make a difference.

Gas additives like acetone are generally credited with changing how the gas burns so it will burn more efficiently. I'm skeptical of most but open-minded. However, I'm also fearful of damaging stuff by putting various abnormal chemicals into my fuel.

No more cruising in neutral, engine off. Thanks! :)

Other than after I've been cruising in neutral, my car has never stalled.

I bet my idling does drive the car a bit, especially downhill at about 30 mph. I haven't made a practice of shifting into neutral at highway speeds - guess I'll have to retest that one.

Good logic about the weight reduction. I suppose that my gf's cavalier would have a much more noticeable effect if I started carrying around 100 pounds for a tank of gas, then retested without.

I figured that most fuel additives wouldn't do much to increase FE, except in very specific situations, or except for expensive fuel additives. Otherwise, why would it not already be added to fuel?

Thanks so far, everyone!

the idea of the higher vacuum is for cruise only. The idea is the higher the vacuum indicates less throttle. There will always be pumping losses especially in an older engine But i've seen 32mpg in my mom's 87 Buick Lesabre driving with a light foot.

Don't forget to rev-match before putting it back in D. This is more difficult without a tachometer but you can at least guess.

Possibly. Most people reporting success are taking 10% or more weight off of small Japanese cars. 100 pounds is at most 5% of the Cavalier.

I have noticed a big difference in my Civic, but nothing measurable in the Odyssey. (2300 lb vs 4300 lb)

A quick google search shows about 2700 lb for the cavalier.

What engine does the Cavalier have? That 2.2OHV is what I would call the little brother to the 3800. It has plenty of torque down low for in town driving and don't see 100 pounds making a measureable difference in that case either.