Oxygen sensor

That's a lot of miles and with it there will be wear and tear cutting down on efficiency. Oxygen sensors, like spark plugs, are wear items. They deteriorate from minute amounts of sulfur and other contaminants in oil and gas. It's not clear if the sensors are the only reason. There may be others like valve clearance, ring/bearing/piston wear, etc.

95 is very close to the 1996 OBD-II requirement date. You may or may not have OBD-II. If you do, then better scanners will be able to show you oxygen sensor waveforms. You can do snap-throttle test, propane enrichment test, etc to check out the sensors. But these are very rough methods, and I don't know, maybe they're good enough.

But with best-in-class Bosch planar sensors about $60+shipping (rockauto.com), replacing them may be more cost effective. That is if the engine is already well tuned. I'd avoid old thimbles whenever possible.

300000 miles or kilometers. At that many miles there is alot of wear, a compression test should be done to see how much real life is left. Sure the 02 sensor can be bad, does it have a distributor so you can adjust timing, retarded timing cut my mpg by 4 on an older camry. When was last tune up, it all matters on a 4 cil. If its 300000 miles, its worn and will be slower.

Thanks guys, Compression test was right up were it was supposed to be, can't remember exact numbers. Just changed out timing belt, water and oil pump and plugs. No change.

300000 miles or kilometers. At that many miles there is alot of wear, a compression test should be done to see how much real life is left. Sure the 02 sensor can be bad, does it have a distributor so you can adjust timing, retarded timing cut my mpg by 4 on an older camry. When was last tune up, it all matters on a 4 cil. If its 300000 miles, its worn and will be slower.

Double ckeck Timing, 1 degree off will mean 1 less mpg and less power. how about a clogged converter, any good tech with a good scope should be able to tell whats up, and thats for timing also incase it doesnt advance right. How often do you change tranny and Differential oil, I use Mobil synthetic and notice a power difference, you checked how wheels spin freely from a rack? What is spark color it could be a weak coil.

Sounds like enough to check for now - thanks

Double ckeck Timing, 1 degree off will mean 1 less mpg and less power. how about a clogged converter, any good tech with a good scope should be able to tell whats up, and thats for timing also incase it doesnt advance right. How often do you change tranny and Differential oil, I use Mobil synthetic and notice a power difference, you checked how wheels spin freely from a rack? What is spark color it could be a weak coil.