I have sorted through all I could find on this topic and I guess I need a little more individualized attention so please bear with me.

I basically dumped my 98 Dakota and bought this 93 Accord because I wanted to save money on gas (my Dakota got 15 mpg). I was very disappointed when my first full tank in the Accord yielded only 19 mpg. In reviewing the forums I see guys that are getting 30 mpg and not many less than 25 mpg.

I called a local dealer whose oil change sticker was on the windshield and gave him the VIN. He confirmed that it had a major tuneup around 3000 miles ago (plugs, distributor, oil, tran fluid, air filter).

I got the car for $2080. I've spent about $350 in parts and several Saturdays replacing bad starter, leaking radiator, bad rear motor mount, and thermostat. I have yet to replace a leaking heater core (bypassed for now) and figure out why A/C doesn't cool correctly. I feel like I have so much invested I can't quit now!

Even with the idle mixture adjustment tweaked (thanks jeffcoslacker) and replaced rear motor mount the damn thing still vibrates like a cheap back massager. I can live with that but the MPG just adds insult-to-injury

Should I cut my losses and pass it on to some other poor sap?

With that much vibration, and after doing the usual fixes, it may be that you just have a weak hole, and you are not running on four strong cylinders. Reasons range from a bad injector to a damaged valve or ring.

The first thing I'd suggest is to buy a cheap vaccum guage ($25 or so) and connect it to a manifold vacuum supply, and check the reading. A mechanically heathy engine will produce a nice rock solid reading at idle. If the reading is within normal range (18-21 Hg), you're golden. The engine is solid, you just have to figure out what's wrong.

If the reading is low but steady, you have low compression throughout all cylinders, or else someone installed a timing belt and muffed the valve timing, or the belt may have jumped (something else you should verify).

If there is a shaking needle or a steady drop on every engine revolution, you probably have compression issues. A steady drop is a dead hole, it has little or no compression.

You can also diagnose a bad cat convertor with a vacuum gauge, it's my favorite dignostic tool. And probably the least used and understood as well. There are always very good instructions that come with the tool, and it's very easy to learn what you are seeing with it. I have the instructions in a picture file. I'll post it if I can find it.

I can't remember if your motor has a counterbalancer shaft that the timing belt drives, but if it does, being clocked wrong can produce tremendous harmonic vibes, and if they clocked it wrong, you can bet the valve timing is probably wrong too...

http://www.automotiveforums.com/vbulletin/http://images5.theimagehosting.com/vacuum gauge.gif (http://www.theimagehosting.com)

Useful pic Jeff, thanks.

Just to get the obvouis out of the way. Did you check the tire pressure? Tire pressure and driving habits have quite an effect on gas mileage

I've been called crazy on these boards for this, but when I replaced the O2 sensor in my high mileage 93 Accord, my mileage went from 25 to 28MPG. Now that it's summer (summer blened gas), I'm getting 29+MPG. Same route, same speed, same distance everyday.

Granted, the old sensor had bare wires showing, but still, that's a nice improvement. I bought a generic O2 sensor and soldered the old connector on to the wires. Only cost me $25 or so off ebay. Paid for itself many times over since then.

Also, what brand/model/size tires are on the car?
Are there any dead hookers in the trunk??