98 escort giving me 15mpg only

I just replace O2 sensor, spark plugs, wire set, pcv valve, Gas filter and still giving me 15mpg only.
Am I missing something?
My escort has 128,000 miles

If you are measuring your mileage on short trips around town before the engine warms up this is what you will get. Measure it on a longer haul with the engine at full operating temperature. To get an accurate figure let the engine warm up. Fill the tank. Drive at least 50 miles. Go back to the original pump and fill the tank again. Don't figure gas mileage while the engine is heating up. It runs way rich until you have put at least 5 miles on it. If you are doing it this way already I suspect that either the thermostat is stuck open (is the temperature gauge going up?) or the sensor for the engine temp that goes to the computer is bad. If the fan runs all the time the temp sensor needs to be replaced.

Check your air filter too.

15 MPG's??? I don't care how cold your engine is, you shouldn't be getting only 15 mpg's at any temp. That's so low that I'd be looking for a fuel leak.

15 MPG's??? I don't care how cold your engine is, you shouldn't be getting only 15 mpg's at any temp. That's so low that I'd be looking for a fuel leak.

I disagree. If the mileage was figured on several short trips of just a mile or two it would give such a low mpg. I've seen it happen on my car. Also, if caught up in traffic on the freeway, it would give such a number, too. When your engine's running and you aren't going anywhere, it is really bad on mileage.

Do you have a check engine light? Have you checked for vacuum leaks? Jack the car up on each corner and check to make sure the wheels are rolling freely. It could be a bad wheel bearing or a dragging brake. I've had brake calipers stick before not letting the brakes release completely. Is the car running smoothly? The 2nd and 3rd generation Escorts also have a common problem with dropping valve seats, causing them to have a knocking noise in the engine and intermittent loss of power before the seat drops completely out and does damage to the head and possibly piston and cylinder wall.

Could be the MAF sensor. When it goes bad the system defaults to a rich mixture. Put a vacuum gauge on it. It will tell you if the seat is going bad on #4. If they valve is leaking the gauge will flutter. The gauge will also tell you if the cat is plugged. It will register 17 inches or less. The fuel pressure regulator could have higher pressure than what is called for. This would make the mixture too rich, also. There are so many things that could be causing your mileage problem.