propane vehicle won't idle

Tweet

I recently removed the demand regulator to access a water pump on a Chevy van. After reinstalling everything the vehicle fired up and ran fine. While on a test drive the vehicle stalled when backing off on the throttle.The vehicle would not restart unless i first press the purge valve. then it will only run if I hold the throttle at about 1500 rpm. It runs fine under partial throttlestalls but stalls at idle.What should I check. Keith