Got in my wife's 2010 LS this morning, tried to start it, got an "ENG PWR Reduced" message on the DIC, and a single click...

After a few tries, pulled the key out and let everything turn off (radio, buzzers, etc.), waited for a minute and it started up, ran like a champ at full engine power...

This morning was very foggy here, 100% relative humidity, are there any known issues with moisture sealing on the ECM?

 

Never heard of any issues with moisture and the ECM, it might be a spurious thing, but I'd take it to an Autozone or other parts store and have them pull the codes to see if its the start of something else. If it has set a code or codes you can reference them when you talk to the dealer since I'd imagine you're still covered by the warranty.

 

I had this problem yesterday at 24 deg F. I also had a low battery and had to jump it. I did try stopping and restarting the engine several times but not the 'let it all turn off' part. Will try that if it happens again though. I also wonder if the ECM was damp inside. Autozone ran the codes and there were several voltage issues and one 'misfire cylinder 3' [p0303?]

Now it runs fine, but I did pick up their $60 code reader so I could read/clear errors. I felt it was worth it since the dealer would have charged more than that to read it once and AZ is not allowed to clear it.

 

I have run in to this myself on my 2.2L LS. What I had to do was remove the air filter assembly and clean the throttle body. What was happening was buildup was preventing the butterfly valve from positioning correctly during the start-up position check routine. It's basically a process your car goes through to verify that the butterfly matches the position that the car thinks it should. Try cleaning your throttle body and see if that helps.