Conundrum, this is without a diagnostic tool other than a voltmeter checking DC Voltage at the ECM connector:

1.Start engine and warm it up to normal operating temperature.
2.Stop engine (ignition switch OFF).
3.Turn ignition switch ON.
4.Check voltage between ECM terminal 23 (Throttle position sensor signal) and ground. Voltage measurement must be made with throttle position sensor installed in vehicle.
Throttle valve condition
Completely closed .15- .85 V (a)
Partial open between (a) and (b)
Completely open 3.5- 4.7 V (b)