Q: Car sometimes give me acceleration and power issues. Engine power reduced message and engine light appear intermittently.

I sometimes experience sluggish acceleration followed by what feels like the car bucking and then "engine power reduced" message appears on the dashboard along with a solid check engine light. The car then feels like it's going to stall so I immediately pull it to the side of the road and turn it off. About five minutes later I turn it on and it drives fine but the engine light stays on. Apparently though, the engine light eventually goes away after a handful of ignition rotations and I can't seem to figure out why this keeps happening.

The first time I took it to my personal mechanic to run a diagnostic test the code came up for the pedal sensor so I got that replaced and thought all was well. However, it just recently happened again and diagnostic tests at both the dealership and where I had the pedal sensor replaced reveal no "error codes" to identify any problem. Why would this continue to happen if diagnostics reveal everything is fine and how should I go about correcting this?

My car has 948000 miles.
My car has an automatic transmission.