Help please -98 Cav Z24. ETS + Hesitation + Loss of Power

Within this past week about 4 times, the cars ETS light will come on. When this happens, the cars rpm's bounce even when holding the throttle steady when up around 50mph (2000-2500 rpm I think), There is a noticeable loss of power and the car is hard pressed to break 50mph. The ETS does go off after a bit, and the car resumes normal functioning.

Testing with an obd2 code reader showed codes 171 and 172, system rich and system lean.

This is my gf's car, and I am not well versed in Chevies (I'm a ford guy) so any and all help would be greatly appreciated.

well when the ETS kicks in, it turns the fuel off going to the one or all of the cylinders, so it will run very lean. Running rich im not sure, the only time the computer will make the car run rich is when you hit the rev limiter and it cuts the spark. Sounds like an electrical problem, those codes are just a result of the electrical problem.

thanks, maybe it ran rich when I tried to give it some gas to overcome the loss of power.