98' 2.5L idle hesitation? HELP!

[SFSTRAT1476]

Hi everyone! Whelp, after a year of ownership and no problems, I've finally hit a snag. First and foremost, a little about my car -- its a 98' with 100K (just hit it this weekend). Got it last year with 84K miles. I'm the 3rd owner and have most, if not all the maintenance records going back to when it was new. I do oil changes every 4k-5k miles.

Recently, I noticed a slight hesitation/sound when idling and a tapping noise coming from the rear. RPM's remain steady at 900ish with no fluctuation. I get a little rattle and white smoke upon startup that goes away once its warmed up. However, I now blow a little more smoke when I rev it up and then let it go back to idle (not belching out smoke, just a steady mist of white). If I try to take the oil cap off, I get suction, but can still remove the cap. When I do, the car bogs down like its going to stall. A little smoke comes out, but RPMs remain at 900ish.

Is my AOS on its way out? I'm not sure if its the original or not.

Also, just noticed yesterday my coolant was abut an inch below the min line. After getting home last night, I saw a very small amount of what I think is coolant dripping form the right rear (exactly where the over flow tube hangs down above the control arm). No leaks in the trunk or under the carpet, but some condensation on the lid just above the oil/coolant caps.

Any and all help greatly appreciated. Here's what I knows has been replaced:

Belt: 94k
Spark Plugs Changed: 96k
Water Pump: 68k
Coolant Reservoir: 70k
Coolant Expansion Tank 83k