Use a diagnostic scan tool to get a readout on all the sensors and make sure they are responding normally. Make sure engine is switching to closed loop operation.
Ok cool, appreciate that. I do have a scan tool, so I'll hook it up and see what the data looks like.
Is it much colder outside than before? All engines do this when it's cold. Engines run faster when it's really cold to warm up. Really cold engines run rich and run fast to counter problems inherit to the weather's effects on the fuel and engine. Fuel doesn't evaporate or stay misted as well in a cold engine in freezing weather, which means fuel can condense on valves, etc. Gaseous fuel burns, not liquid fuel. Running faster causes the fuel to vaporize more readily by the vacuum of the engine running against the closed throttle valve. the RPMs will drop on their own after a couple minutes as the engine warms up.
It is colder, yes, so I can see where you're coming from there. That would make sense, thanks!