I have a 2010 G6 with the 2.4L motor. My car is randomly having this weird engine power reduced issue, it usually happens after I have been sitting in park for a few minutes, or at a red light, but has also happened when I go to start my car in the morning. Happens about once every 2-3 weeks right now. The only way I have found to fix it is to shut the car off and back on a few times. Sometimes I get a check engine light after, but if I shut the car off and on again it goes away, I had the code chekced once and I forgot to write down the actual code, but it was related to the throttle control or sensor. Basically the message comes on, the engine feels like it has no gas or power and shakes really badly, usually I can pull off the road, or into a parking spot, luckily it hasn't happened at anything over 5-10mph.
I don't know if it's related or not, but back in August I took my car in for an oil change, somehow they accidentally cut a wire in the engine bay, when I started my car after the oil change the engine "Engine Power Reduced" message was displayed with the same rumbling rough motor issue. I shut it off, went back in and they pushed it back into the bay, and found a small wire that was cut when he was wrenching. They used a heat shrink thing and electrical tape and repaired the wire. Here's the area with wire they fixed: http://i.imgur.com/IPJvcC0.jpg
After they fixed the wire, everything seemed fine, until about a month or two later and it gave me the same power reduced message. This time it was right after using one of those gas treatment things from AUtoZone, again no idea if that was related somehow.
Since then it's happened a few times, usually at low speeds, or while idling at a red light. One or two times I have gone out in the morning and it won't start right away, I get the message, turn it off, wait a minute, and it's fine turning back on.
I feel like it could be related to the wiring, but I honestly have no idea. Any other ideas besides the wiring that could be causing the issue? I can't really recreate the issue for mechanics since it's random, so it's been hard to diagnose.