i need help with an 89 chevy truck that starts but wont idle?

Could be a fuel leak just above the fuel pump in the tank and when the throttle is released ,because the leak causes loss of fuel pressure the engine dies.Could also be defective fuel pump.Could also have a broken wire inside the insulation next to water temp sensor on top of intake manifold.That would cause the engine to die at idle as this is cold start signal for warm up mixture to computer.EGR system may be defective at vacuum control solenoid causing engine to die.

sounds like your throttle position sensor

sounds like your throttle position sensor