02 Cavalier with 178k. I’ve never had any problems with the engine–yet. I noticed this morning it was sputtering while idling, in park or drive, like a drip coffeemaker maker spitting out the last of the coffee. When it goes on for more than 10 seconds or so, the needle on the RPM gauge starts to wiggle up and down. When I tap the accelerator, it goes away for a few seconds but then comes back. It might be doing at while moving too but more gently. My mileage is the same as ever, up a bit if anything. Any ideas?
I think your car has what’s called surging.
It could be a vacuum leak, dirty fuel system, dirty idle air valve, stuck thermostat, or something else specific to this model.