Question for Mazda Service Center

I owned a 2nd hand Mazda 323 Familia "96 model... I'm experiencing frequent stalling during traffic, frequent engine shut-off at uphill (coming from pull-stop "bitin"), sometimes engine surging at high speed (highway) & poor idling (accelerator gauge are moving up & down). I've found out that the 3 wires on my throttle position sensor had a volts reading (5.1, 4.88, 4.98) when I test it with digital voltmeter. Was there a problem on my computer? or grounded somewhere on my wiring/sensor?