computer readout says random ignition on cylinders 1&4. What is most likely fix? on 1999 Buick Park Avenue

Car runs but mileage has dropped from 32mpg to 18-20 mpg. Cylingers cause terrible idling and difficult to start from the stop sign due to no power. Engine vibrates due to cylinders not firing. He needs car for a couple of hours to diagnos problem but can't get car in for 10 days.

Asked by for the 1999 Buick Park Avenue
It's going to need a Tune-up most likely, so Plugs, Wires, and a fuel injection service.