Lincoln towncar stall

My 1994 Towncar has 150K miles. And has had a problem for a couple of years now that has progressed to me not driving it any longer. It used to stall after it had been running at high speeds for a while, and then came to a stop. There was a low whistling noise that came from under the hood all the while. The whistling noise continued to get louder, and the stalling became more regular. After I cranked it three weeks ago, the whistling sound was noticably 3x or so louder than it was when I parked it, the engine idled rough, and then cut out. I still drove it for another week, but parked it b/c as I slowed to stop, I had to shift it into neutral to keep it running, and if the rpms got too low whille I was making a turn, or whatever, it would cut out while rolling. Now it will crank, but will not idle. The engine will continue to run if I keep a little pressure on the accelerator, but otherwise it will not stay cranked. I replaced the fuel filter 3mos. Ago, and again 3 weeks ago, in addition to replacing the air filter and the spark plugs. Is ther a Idle screw? Idle pump? Or idle motor? And why does it seem like the whistling noise(compression) is related to the problem? It performs well as long as my foot is on the gas. The whistle stops when accelerating.