KPHL 2004 flying CRJ200 (CL65) - similar type. 10000 feet inbound for landing, 300 hour copilot slaps throttles back to idle. Single Engine oil pressure light illuminates as engine spools down. Declare emergency and proceed with engine restart checklist. Engine restarts and continue with normal landing and shutdown. Turns out throttle was rigged incorrectly. Missed clue that throttle had to be advanced slightly forward of idle stop to get a light off during startup. FCU did not meter enough fuel to maintain idle when throttles were moved abruptly back to the stop. Dual engine failure would be challenging at low altitude - took almost 30 seconds for restart on one engine. Note - Philly ATC put us back in line when we notified them of engine restart.