Throttle does not return to the home position thererfore the engine revs high. Revs correctly when I pull back on the foot pedal or pull the throttle back. Cleaned spring attached to throttle and this worked temporarily.

What is the car? This sounds like it could be a throttle position sensor, (TPS). This monitors how hard you are pressing the gas pedal and if it is faulty it won't be reading the pedal movement correctly. Other symptoms are uneven idle and the acceleration isn't smooth or even.

I suspect there should be a spring to return the throttle lever to the idle position. Without the spring, the throttle plate will stay open and allow the engine to run at high rpm.

Is it possible the clutch pedal is interfering with the throttle? Start the engine in neutral and allow it to idle. Press only the clutch pedal down and see if this increase the engine speed. If it does speed up the engine and slows back down when you release the clutch then somehow this operation is where your fault lies. If it doesn't alter the idle speed, then rev your engine and release the throttle to see if it returns to idle immediately. If it is slow to return to idle then your throttle cable could be sticking. This means when you change gear lifting off the throttle has little effect and depressing the clutch to change gear causes the engine to race as the throttle is still partially open.

May be throttle position switch needs to be replaced.

The spring or wire that connects your pedal to the throttle body may broken or damaged. Check under your hood and look at the throttle body (it's the carburetor looking thing). There should be a steel wire connected to it coming from the back of the engine bay. It should connect on the side where you'll see a few springs. If nothing looks broken there, turn the part of the throttle body connected to the spring and wire. If it revs up when you move it, then the cable could be broken somewhere between there and the gas pedal.

Alternatively, the linkage on the pedal could have been disconnected some how. Check behind and above the gas pedal to see if eveything is connected properly.

check throttle positioning sensor or mass air flow (maf) sensor

first off.... does the engine over rev on its own? or only after you press the gas pedal?
does your vehicle have a throttle body that is electronic or cable actuated?..if electronic and revs on own could be one of two issues 1) throttle body itself 2)throttle pedal switch on gas pedal)
if cable and revs after pushing gas pedal ..either there is too much carbon built up on the throttle plate or the throttle cable has begun to fail.. remove the intake tube from the air cleaner to the throttle body and inspect

my 1990 toyota starlet idles fine its when i put my foot on the throttle it revs up then drops down by itself even when my foot is to the floor

Have you tried checking your throttle positioning sensor. Possible vacuum leak or check for carbon build up in the throttle body not letting the throttle valve shut all the way.

if you can pull back on the gas foot pedal and it will idle better then it might of just started doing this. spray some throttle body cleaner inside the throtle body where the throtle opens and closes. build up should be the first cause because it wont let the throttle plate close. other wise check for a vacume leak.