Car question

[glatt]

Well, the roughness seems to be not so bad the last week or so, but I'm not sure. The roof used to buzz from the vibration and that's not happening recently, but there is still some roughness in the idle after it warms up. You can feel it in the steering wheel and the cds in the door pocket rattle. It still goes away when you give it some gas.

I have old records of the mileage from when this car was new and I was better at tracking that stuff, and I can compare that to the mileage the next time I fill the tank, but keep in mind that gas didn't have ethanol in it back then, so it would be comparing apples to oranges.

Is it worth it to buy a bottle of fuel injector cleaner and dumping that in the tank? Would that harm anything other than a few wasted dollars?

Also keep in mind that we don't drive much. I take the subway to work, so it might be a couple weeks before we fill the tank again.