86 mr2 starts but will stall if not giving it gas with the pedel.

SOURCE: starts but does not stay running

check main relay

SOURCE: Head gasket was leaking on my 86 mr2 Replaced the

Check all the wiring connections that you loosened or took off when you removed the head. something is loose or disconnected ,eg., ground wires .
Make sure you have spark at spark plugs whemn cranking ,and fuel pressure.
Did you try spraying starting-fluid in the intake, see if the engine runs for a little bit.
Compression to be anything above 100 psi will firean engine ,sometimes lower too.

SOURCE: starts then stalls

Sounds to me like a fuel related problem. What i would do first is check fuel filter then air filter. Check TPS (throttle positioning sensor)<<< that is my guess not seeing the car and also check fuel pressure. Fuel pressure should be around 40 to 55 PSI

SOURCE: engine stalls when foot not on gas pedal

sounds like a large vacuum leak to me possibly a bad mass airflow sensor but i would pinch off vacuum lines maybe spray a little carb spray around throttle body and intake area to try and locate any vacuum leaks

SOURCE: my car starts up n run for thirty seconds then

Shortage of fuel is your problem. Please make sure that enough fuel is reaching the injectors/cylinders . And while you are at it please clean the air filters as well.