1992 Mercury Marquis Overnight engine change. Rough idle

A 1992 Mercury Grand Marquis ~100,000 miles. Engine was running perfectly. I brought my car in for annual inspection. Asked that the oil be changed. The freon level to be checked for my air-conditioner (he added 1/2 lb freon) and to check the light switch (my headlights were
beginning to blink on and off). They ended up pulling the light switch and cleaning it. Headlights seem to work fine now. But the problem is that the next day when I picked up my car the engine runs rough (especially under an air-conditioner load) and the car 'jerks' when the transmission is shifting gears (especially if I transition through the lower gears slowly). It seems that the idle of the
engine at a stoplight is uneven and changes whenever the clutch of the air-conditioner kicks on and off. I guess that I feel the rough engine 'miss' mostly at idle. But in fact, it feels that it is happening at all speeds.

thanks,
barry