Try your AFM. Air Flow Meter. This is the box right beside the air filter. It controls the amount of fuel goinging into the car in relation to air coming in. If it is malfunctioning then it might have the car running rich giving you your bad fuel mileage. Also try cleaning your throttle body. I will keep working on it!

 

I'm not a Celica driver but could it be the cat? Dunno if that year even has one but if so, it's definetly a possibliity. Other then that, the coil, wires, fuel injectors?

 

Sensors

The air mass meter could be your problem, but by what you are saying it sounds more like the the coolant temp sensor. When the engine warms up the sensor is not picking up this increase in temperature therefore tricking the computer into thinking that the vehicle si still cold and inreaching the air fuel mixure (poor fuel efficiency).

Hope it helps.

FAB.

 

I cleaned the AFM and the whole intake up to as far as i could into the EFI but i think it might be a little dirty up in the efi even . what would be the best way to clean into the efi. when i cleaned the AFM and soo on it made my car run better as far as i could tell for the little drive i took it on. I am thinking the injectors are possibly dirty a little as well. Thanks for the tips if there is anymore ideas i would GREATLY appreciate them i really want my good ol Celica back and running decent. That cars been through alot but i know its got lots of life left in it. Damn Good car.

 

fuel problem

I agree with the air flow sensor causing your problem.
Although if the problem occours after the engine warms up it may be a problem with the 5th fuel injector this injector is located on the top right side of your EFI air plenum, it works like a choke on a carburated engine, It is also called the cold start injector when the engine is cold this injector is in service allowing more fuel into the engine it is controlled by a water temp sensor located below the top raditor hose where the thermostat housing is. Below the thermastat housing you should see 2 electrical plugs 1 green and 1 brown which one is for the cold start injector I would have to refer to the manual.

Easy test carefully remove the wire retaining clip from cold start injector plug after the engine warms up and starts running rough unplug the wire from the cold start injector if the engine smooths out then I belive you found your problem.

If you need more assistance let me know.


PS just a little something that might save your engine
Change out the Oil pressure sending unit I lost an engine due to mine blowing out the bottom half of the sensor and dumping all of the engine oil on the road.