I DID A MAJOR TURN UP ON MY COROLLA. AND NOW MY MILEAGE WENT FROM 30 MILES TO THE GALLON 12 MILES TO THE GALLON. I HAVE NO ENGINE LIGHT ON. PLANNED YOU TAKE IT TO THE TOYOTA DEALER BUT HE SAYS WITH NO ENGINE LIGHT ON WE CANNOT HELP. I AM GOING TO CHANGE THE OXYGEN SENSOR TO SEE IF THIS HELPS OR NOT. MY CAR IS A 1994 TOYOTA COROLLA WITH 195,000 MILES .
Could you describe exactly what you did to the Corolla? Major tune up, or tune up in general, is a worthless term these days and can mean many, many different things to different people. If your gas mileage problem started immediately after you did work to the car, the problem is a result of something you did to the car. Also, hoping to solve this problem by throwing an oxygen sensor at it is hoping for a miracle.
What parts did you replace ? Did you use OEM (Toyota) parts or aftermarket ? Besides the bad mileage, how is the car running ?
What spark plugs, wires, and cap and rotor brands did you use? Toyotas love NGK plugs, but hate Autolites. Bosch plugs seem to do OK, but Champions are just as bad as Autolites.
I think you just need to change the thermostat. Next time you drive the car, check the temperature gauge after about fifteen minutes of driving. If the gauge is to the left of center, the engine is running too cool. Your engine needs to run hot to be efficient, and a too cool condition in the engine will prevent the transmission from shifting into overdrive at higher speeds.
A cool engine and the loss of overdrive will kill your gas mileage, not to mention your engine, especially if you need to drive at highway speeds. The engine will continue to run at much higher revolutions than it needs to until the temperature gauge hits the halfway point. That means your engine oil will break down faster and the engine will wear faster.
It’s spring now. With the warmer weather I think your car all at once is going to be much more efficient. Also it going to feel a lot different on highways, less strainy.
If so, be proactive and change the thermostat out with the old radiator fluid.
How did you determine 12mpg?
Did you double check the gap on the plugs to .032 ? or just trustingly throw them in right out of the box ?