O2 sensor?

There are alot of things covered in a tune up to affect milage, 1st is cold weather. Putting it on a scope will determine if o2 sensor is bad. Second check timing. After a regular tune up and synthetic oil everywhere even differential, trans and power steering once I went from

20-30 , alot of small issues affect 4 cil toys.

Cold midwest US weather always drops my milage easily 20%+.

That happens every year. I'm near the MA-NH border and it does get cold here.

Cheaper to just replace it ($20).

Nothing has changed the timing in 10 years. I'm not going to noodle it.

Modern cars don't have anything to "tune up". The computer(s) take care of it. You twist 1/4 turn and the computer twists 1/4 the other way!

Maybe new plugs will help however. 146,000 miles on the first set. I could have a bad one!

Yes. Different lubricants might improve the mileage, but doesn't account for the decrease.

I just discovered that my tires are a bit soft. I'm sure that accounts for a bit of the decreased mileage.

Thanks for the check list. I'll bet plugs and airpressure will bring the charriot back to normal.

Gee stubby you have alot to learn , timing belts stretch retarding timing, retarded timing lowers plug cilinder temp, increases pollution, carbon buildup, mileage and reduces power. A 3-4 degree retard on my 4 cil, and 3-4 is normal on a belt of 60000-80000, reduced my power dramatcly and mpg by exactly 4 mpg, yes Four.

Old plugs electrical resistance to fire increases and electrode wear affects burning and combustion efficiency , as well as it affects timimg when gaps widen enough. If I replace a 30-50000 mile set I feel more power and see 1 - 2 mpg every time.

Wires increase resistance as they age, caps carbon track and pit as does the rotor, I easily get 1 mpg on a new set.

A bad PVC valve can cost you 1-3 mpg from not recycling blow by and ruin oil fast.

A dirty intake causes loss of power

An old thermostat that opens early or never cloes will loose you easily

10 % milage when its 10f out and you drive short trips.

A weak coil not providing blue spark will cost you in milage.

Old calipers can stick causing brakes to drag, and the list goes on. The computer only adjusts within a parameter it cannot make up for timing being off as mechanical timing is its set point. I got my 4 cil

91 up to getting 36 last summer on a few trips, down from a low of 20-21 in winter, there is indeed alot you can do. Normal ran out 9 years ago on your 95, noodling as you say only restores factory parameters. After market wires and thermostat are crap, I never get more than 30000. Synthetics like mobil in trans, differential and motor will alone see you 3 mpg, With my 91 every day in summer I get 28- 31, 35 on trips, but winter is another story

I know that.

Is it a belt or a chain? I actually have that changed every 100K, but that's not a "tune up". I get a new water pump at the same time.

OK. I'll find my old timing light and check it. How many degrees is right?

If the gap is wider, it will indeed take a higher voltage to breakdown the gap. But if the coil is good, the difference won't matter. 30kv is going to make a spark no matter. Try holding a plug wire near the engine so you can see how far the spark will jump.

I don't see how the very slight difference in the time to jump the gap can affect the timing. How many microseconds will, say a 50%, gap increase delay the spark and thus the timing?

If I replace a 30-50000 mile set I feel more

You're lucky.

Wires normally run about 100K. When they get "bad" according to friends, I've measured them at 1M. When all else fails, I'll change the wires.

Good point. I'll replace the PCV and try it out.

True. Whenever I find air filters on sale I change it. Probably once

1 year but I've never been able to say that it increased my mileage.

As long as the heater works and the engine comes up to temp, I assume it OK.

True, but coils really don't fail often. You can test it by turning off all the lights and running the car in the dark. Any sparks or glow means it's bad. I knew a guy that used to insist on "cleaning" his coil with all sorts of solvents. I believe he was actually providing a conducting path!

Yep. The brake heats up and you smell it! I've had that happen.

and the list goes on.

I think I would like to own an auto parts store in your town!

Where are you located? Does the area you are in run oxygenated fuels? I always get reduced mileage with the winter fuel blend here in Colorado.

Before you replace the O2 sensor, test it. the factory service manual gives the procedure. use the OX1 terminal on the underhood DLC (date link connector) near the passenger (US) side strut tower one side of a VOM probe goes to the terminal, and one side to ground, then you count the number of fluctuations over time to see if the O2 sensor needs replacement

see:

For airflow I meant a dirty throttle assembly , at least that is what I think its called on a 4,

I dont know timing for your year. If you only have 20 thousand or so im sure its ok but checking is always a good idea, be sure to short the proper terminals.

Coils on the 4 are a known issue of problems.

For temp its something you will notice that it takes longer to heat then it used to.

I actualy have poor auto adjusting on one rear brake and it adjusts till there is drag, something I have to fix, and I get no smell..

Point is alot of little things add up on the 4, nothing I really notice as bad but when done my mileage improves, as another noted winter gas mix can hurt mpg, but bigest factor is just the cold short trips.

Thanks. I snatched the whole manual, also. That will save some trips to the library, not to mention copier expenses.

That sounds about right. The engine burns fuel most efficiently when it gets up to normal temperature, and it takes a lot longer to get there in cold weather. It's best to minimize the number of trips you take in your car on cold days to save gas.