My Car: 1990 Nissan 240SX, Automatic, KA24E.

Body: 190,000 Miles, Motor I'm told has about 90,000 miles and was replaced a few years ago.

Questions:

1) Car seems to have a rough idle and fluctuates between I would say 500 - 800 RPM at idle. I changed the Spark Plugs Today, Wires will be changed tomorrow along with Distributor Cap. Any other recommendations? I know the Air Intake has some Black Tape wrapped around at some parts, could their be a leak? I've also heard of the Air Control Sensor, EGR Valve, Fuel Filter, Etc. So I would like the Pro's to tell me, what do I need to replace to give this car a really good tune-up?

2) When I am in PARK, I rev up to about 1.5-2000 RPM and I hear this rattling coming from somewhere, can't tell if it's the exhaust or the motor. ALSO, when the RPM's begin to drop, it hits around 1k RPM, sometimes I hear this grinding sound, almost the sound of a fan or something scraping something, but sometimes it doesn't do it. Any idea?

Standing by for Answers, will Give Rep!