My 2010 G37x accelerates really slow but eventually gets speed. I made a mistake and put 87 in about 2 weeks ago. I've always ran 93. but I ended up in this small town that just had regular only. I've cleaned the throttle body and performs a little better but not as normal. I did notice when turning corners it jerk so I feel like it gas related. I did top it off twice no change. There's no CEL showing. Also I noticed some weeks ago that it will start without pressing the brake but my brake lights work fine. Anybody experiencing this problem?

 

If you can start your engine without ever touching the brake pedal then more than likely there is a problem with the brake pedal switch. While your brake lights might function as normal, these switches handle more than just your brake lights and, as such, there could be a intermittent short, corrosion, or other issue with the switch. This would also explain your lack of power/ jerking/ drivability issues that your are experiencing as your car is receiving mixed signals. It has happened before where TCS cuts power under unusual conditions. I doubt your issue is fuel-related.

Look under the dash and check all of the brake pedal switches- there are two (2): 1 brake and 1 ASCD. Make sure connectors are clean and tight and that the switches are solid in their brackets. There are small rubber pads that contact the switch plunger- these are known for deteriorating and breaking off. Depending on your skill level- and if you have a digital multimeter- probe the switches for continuity. Worst case scenario replace the switch(es).