Anybody experience a change in engine RPM for first couple seconds. 1023E has always start right up at 1500 RPM idle right from the get go. The last two times on initial morning start up the engine does 500 RPM for a couple seconds (a little stumble) and goes to the normal 1500 RPM idle. Any restarting during the day is normal at 1500 RPM's idle. The next morning it's the 500 RPM stumble and goes to 1500 RPM's. This is all in warm spring weather. What's wrong here?