rough idle

I have a 94 GT with about 154,000 miles on it. When I'm at a stop, the car idles pretty rough to the point that I can feel the car shaking. When I look at the tach I can see the needle surging up and down between 600-800rpm. The idle air control motor was replaced less then 10k miles ago with an oem motorcraft part. The check engine light never comes on. Should I start by doing a tune up, replace plugs, wires, cap, rotor, and fuel filter? Any other suggestions what could cause this?

Good suggestion with the balancer. I'll check that out as well. It was recently replaced with a motorcraft balancer because of a bad vibration, but it's possible it might be bad again. I've heard SN-95s tend to have balancer problems? I'll try pulling codes too and see if I get anything.

The shaking feels more like someone is on one side of the car and is pushing on it to rock it back and forth from side to side.

A tune up is definitely in store, going to order everything from rockauto.com this weekend after I get paid. I was able to determine part of the problem tonight. The vacuum hose that goes from the back of the intake to some sort of electrical sensor towards the firewall on the passenger side was all cracked (another section of hose continues from the electrical sensor to the passenger side strut tower). The car is idling much better now.

There is a new problem now that just seems to have started tonight. The car stalls every once in awhile with the air conditioning on. It doesn't always do it but sometimes I can be idling at a stop light, flip the A/C on and within 10-15 seconds the RPMs will drop slightly and it's like it can't compensate so the RPMs continue to drop and the car stalls. It doesn't do this when the A/C is off. My first thought is bad IAC but I replaced the IAC with a motorcraft unit about a year and a half ago, less then 20k miles ago. What could cause the engine to stall at a stop when the A/C is running?

Thanks for the link, that's exactly what I'm referring to. My hose going to the back of the upper intake is starting to shred. No way in hell I'm removing the strut tower brace or the upper intake the repace that vacuum hose. I was able to bend my arm and reach almost all the way back to where the hose attaches to the vacuum port. I'm going to attempt to fix it with everything still intact.