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The problem is on a 1994 sportrak 1.6 elxi.
I changed the coolant sensor and the engine runs so much better from cold and spot on when warm , no engine light on .
However from cold it runs badly at low rpm ( 500 or below), and pressing the accelerator then letting off sometimes results in the engine stalling as revs drop too low. When the engine is warm the idle returns to 900rpm and runs perfectly. My other sporty hasnt this problem as the rpm stays high for a minute or so before slowly decreasing - warming up cycle.
why doesnt my sportrak have this kind of warm up cycle 
Right, to begin at the
Right, to begin at the beginning, injection system.
Locate your throttle position sensor and check this, it basically works by having a switch which activates at idle which switches the ECU from a running map to an idling map when the throttle has no weight on it. AS you press the throttle it moves off this switch and moves across a variable resistor which obviously gives a variable resistance depending on throttle position, and if you give it full throttle it hits another switch and gives it full bananas.
To test this you need a multimeter and identify the correct wire, press the throttle and then release it and it should either open or close the switch depending upon type, if it does nothing then it could be faulty or need adjusting to correctly position it so this switch activates when the throttle is closed.
Check for minor air leaks on the inlet side as any of them can cause this, and it may only be the smallest of air leaks.
Check the mass air flow meter, if it is a hot wire type then it may require cleaning, if it is the volume type with the 90 degree plate then it may need cleaning or be sticking.
Check the ignition timing.
If the system has an ISCV (idle speed control valve) then check this, or ideally replace it with one from another vehicle known to be running correctly to test it.
so how do you test
As far as the throttle position sensor goes i am confused on how you test it
Am i right in thinking its the black box like thing which slides onto a shaft coming off the side of the throttle body with three pins coming out of it 
Same problem
hi i have same problem but i think im the cause recently had head gasket failure on my car stripped head off and re-built new bits in flushed cooling system etc and basically when putting back together found myself with a spare vacuum hose lol car starts after about two cranks but idles at around 600rpm and any hard reving followed by depression of pedal causes it to cut out...
igntion timing is sound vacuum that spare comes out of inlet manifold on the engine side but cant remember where it goes... so far distributor vaccum, fuel pressure regulator 3 hoses on top of throttle body, power steering etc etc all plumbed in but theres this one vacuum on inlet that floats around when i hold finger over the hose engine is less lumpy but still sits at 600rpm...
think idle control valve but not certain of location or if even fitted as mine in 1991 model... if anyone has any ideas please let me know!!!