You might want to look into the oxygen sensor. After 140000 miles, there is a good chance that, although it may not be dead, it may be sufficiently weak that it is causing a rich running condition. You might just want to go ahead and replace it. ESPECIALLY if it is cheap. You might also want to check the catalytic converter. Now I don't know anything about Metros specifically. But automakers have a NASTY tendency to use close-coupled cats (cats mounted directly to a short exhaust manifold and located right in front of/to the rear of the engine) on cars that are built for high fuel economy. Since cats that are THIS close to the engine tends to get REALLY hot exhaust, close-coupled cats have a tendency to deteriorate prematurely. And a clogged cat can DEFINITELY rerduce fuel economy. Take a look through it with a flashlight to make sure it is not clogged.
I believe the factory recommends 5w-30 and they hold around 3.7 qts of oil.
This may not effect mpg too much, but you should clean the egr valve and passages thru the head. Metros are know to burn exhaust valves when the ports plug. Check out http://www.teamswift.net/viewtopic.p...&highlight=egr for specifics on this and other info.
What kind of mpg are you getting now?
Best tank= 81.23 mpg on july 1st 2008
SAVE SOME GAS, SAVE THE WORLD!
A good tune up would be plugs, distributor cap/rotor, and fuel filter. I normally change plugs at about 20k, cap and rotor at 20k and fuel filter at 50k. Air filter I change when it is so dirty I can't see sunlight through it. I never change the wires unless they test bad.
If you still aren't getting mileage in the 40mpg range then check your sensors with a voltmeter, there are not that many of them so they are pretty easy to check. The oxygen sensor is like 17 bucks so it is not really worth taking it off to test it, just replace it. Get a vacuum gauge from autozone/advance or one of those types of places ~$20 and stick it on the dash to monitor the engine. The needle should be as smooth as possible with very little vibration, the more vibration you have the more likely something is wrong. Set your timing to 8 degrees instead of the recommended 6 degrees. All that should make sure your engine is running as good as possible.
As far as the rest of the car, check your tire pressure and set it to the max sidewall pressure. After driving for about 20 minutes check the temperature of the rims around where the lug nuts are and the front rims should be slightly warm and the back should be cooler. If one side is warmer than the other front or rear then you have a dragging brake or bearing.
Once you get it in the range of 40-45mpg tanks that is about what the car got stock. Then it is time to start modifying it to get as high a mileage as you can go.
change the tranny fluid, it's commen to forget about, we put amsoil 5w 30 Manual Transmition Fluid in our metro and it seems to have liked it (over 50mpg last tank), but for the most part just do a tune up.