1997Ford Taurus- rough idle

My 1997 Ford Taurus has idled rough since last September. Have had it to two mechanics. First one told me it was dirty injectors and suggested my using injector cleaner in the gas which I have done since first of October with very little, if any, change.
Then this last week another mechanic checked to see what the problem could be. He said he checked all sorts of things that might be the cause of the problem (vacuum hoses, spark plugs & wires and I have no idea what else ???). He also said that he did not think it was the injectors.
What would you suggest? Or is it even a problem that I need to be concerned about? Would using a higher grade of gas help?
Thank you for any help you can give me!

does the car run better at higher rpm or worse. could be a MAF or clogged injectors, or a vacuum leak . if the car runs better at higher rpm then it is prob a vacuum leak and you can test this by spraying carb cleaner around the engine while at a itle and if it idles up higher then your leak is there. If it runs crapier then prob a plugged injector or maybe a faulty fuel pressure reg or pump. highly bad or old gas even. If the gas is considerably old I would drain it and put high octane in it and run it for 15 mins to clear out the old gas

a common prob with this year is failure of the MAF sensor. this is located on the intake pipe after the air filter and before the intake manifold. It is round and has wires to it. The intake goes through it. Find it and then unplug it and see if the car idle changes iof not that is your prob. This is a spendy part I would look at junk yards www.car-part.com or ebay.