Loss of power and running rough

What has been done so far to solve this? Has a mechanic been involved or have you just continued driving? Have the diagnostic fault codes been read and recorded? If so, what are the code numbers?

First of all, you are supposed to stop the engine when the check engine light is flashing. The flashing light means too much unburned fuel is going into the exhaust system where it will overheat and damage the expensive catalytic converter. The first thing a mechanic will do is read the diagnostic fault codes. Those will indicate the circuit or system that needs further diagnosis, or the unacceptable condition. Any time the check engine light has been on, there will be a fault code in memory. There can be codes stored in memory even when the check engine light was never on.

If there are no fault codes pointing to a sensor circuit or other suspect, the mechanic can use a scanner to view live data during a test-drive. If he can get the problem to occur, most scanners have a "record" feature that allows him to record a few seconds of information that can be played back slowly later to see what changed. The problem is there will not be anything to point to a suspect circuit if the engine is running normally. That is where the fault codes are valuable clues.

The people at many auto parts stores will read codes for you for free, but remember, they are in the parts-selling business. Fault codes will never ever say to replace a part or that one is bad. Here is the link to the list of codes and their descriptions:

https://www.2carpros.com/trouble_codes/obd2

and as you can see, they only point to the circuit that needs to be diagnosed. If your college or a nearby community college has an automotive program, they can read codes for you too, and they might be willing to work on your car, but you have to understand they are taking work away from the area shops, so they will only take in cars with engine performance problems when that is what they are studying. They wont look at your car during "brakes" class, for example. Also, they have to squeeze your car in when time allows between class periods, so you might have to leave it for a few days. If they can do anything, it will cost a lot less than going to a shop.

Regardless where you take it, reading and recording the fault codes is the place to start.