Will not idle, it stalls, its right back up and unless I apply gas it'll stall

I have a 2003 gmc sonoma pick up, 6 cylinder automatic. When I get up to go to work itll start right up but will not idle, it stalls, its right back up and unless I apply gas itll stall. Once im driving its fine but I have to pop it in neutral at stop lights with my foot on the gas to keep it running, After about 20 minutes its fine. The check engine light is NOT on. The guy at auto zone check for codes but found nothing. Also, when this happens my fuel gauge drops to empty. No other gauges are affected, just the fuel gauge.