The flickering light is telling you the oil pressure at idle is very low. This could be the fault of the sensor, but to test it you'd have to take it in and have a mechanic check the oil pressure at idle on a real gauge. Since the oil light is off when you step on the gas and the motor revs up you really shouldn't have a problem. It is very likely the oil pressure at running speeds is low too, but enough oil is moving around to do the job of lubrication.
If you want to pull the pan, you could clean the gunk and sludge out of the pick up screen. On an older car there is a good chance this is part of your problem. Otherwise just keep the oil level topped off and perhaps move to a heavier weight oil in hot weather. If you are running 10W-30, try 10W-40 and see if makes any difference. If you haven't changed the oil filter in a while, perhaps the filter is clogged and reducing flow, another cheap thing you can do yourself.