Ok this is odd and has me confused. I just tried checking the IMG with propane, had a new tank of propane and the nozzle with a hose on the end and ran it around the gasket, unlit, with the engine running but the idle never changed. So to see what would happen if there was a leak I unplugged that vacuum line the shift actuators, felt it had vacuum and put the end of the propane tank nozzle over the hole and the idle didn't changed. So with the propane on a known vacuum leak the idle still didn't change, the idle only changed for a second when I unplugged the vacuum line but went right back to normal. So I don't know but propane had no effect on my idle.