Vibrations around 1700 rpm, balancer replaced...

I replaced the harmonic balancer last night, thinking that'd solve my vibration problem. It definitely helped out, but today on my way to work I noticed that it still vibrates once in awhile around the 1700-2000 rpm range. The new balancer is in fine, and doesn't wobble at all, so I'm wondering if it has something to do with my driveshaft or u-joints? The vibrations pretty severe, it feels like the car just studders a lot when it happens. Also, my timing's currently quite off because of the old worn-out balancer, and previous owner's screw up. It's getting fixed tomorrow, but I'm wondering if any kind of misfiring could result in that bad of a vibration? Thanks a lot,
-Jeff

Thanks a lot for the replies. I replaced the upstream O2's last night also, along with dizzy cap and rotor, thinking my CEL was from the old O2's. After disconnecting the negative battery cable for like 10 minutes, I drove around my neighborhood testing speeds between 0 and 40, getting it up to 4k a few times, the spot where it used to throw a CEL. I got no CEL from any of this, until a couple hours ago during a drive to a friend's house when it came on and stayed on until I stopped. And in response to the vibration vs. studdering, it's definitely a studdering. Happens around 1700 rpms in all gears, so would that mean it's driveshaft related? Taking it to Race Related, a local shop, tomorrow afterschool. The owner said he'd fix the timing for no charge, and also look into the other problems I'm having. Also, if it's any help I'm running 93 octane, and at idle my car literally sounds like it's cammed. Would that mean the timing is advanced or retarted? I'm also not sure about the EGR. I plan on dumping the codes tomorrow.

The_Mustang said:

Give us some insight as to how this vibration came up. Like, did you do any work on the car around that time? Any other parts fail at or around the same time?

Generally the driveshaft will only vibrate as you get to higher speeds and is NOT RPM specific. Do this, try to achieve the same speed in all gears no matter the RPM, does it vibrate? Next, achieve the same RPM you get the vibration at, no matter the speed, does it still vibrate? You need to isolate the problem; Driveline or Engine.

My car was studdering pretty bad and it turned out to be the PIP sensor in the dizzy. Just food for thought.

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It must be engine then. It's RPM specific (~1700 rpms). As for recent parts replaced, after first noticing the problem, along with wobble in the balancer, I replaced the balancer, dizzy cap, dizzy rotor, and upstream O2 sensors. I've also recently started running pretty rich... Sounds EGR related? By the way, I really appreciate all the help I've been getting from this forum. I'm just trying to get this car back up to good factory specs for the time being, and it's a hell of a learning process lol.

The_Mustang said:

Well, if you can't get it sorted out eventually, Largo is only a few hours away.. I'll come help you figure it out!

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Damn man, I really appreciate that offer. Good news is though, I took it up to our local Mustang shop around here and had it worked on for a couple hours. Turns out that CEL was from a bad EGR, the "taking a dump" factor was a horribly dirty MAF sensor, and my idle was caused by a couple vac leaks. Everything got worked out other than the EGR, which will be disabled next weekend or so probably, and the car runs like an absolute dream. The OBD programmer or whatever it was the guy had plugged in showed that all the cars 'vitals' were in great shape, and I can't be happier with it now. Thanks a lot for the responses I've gotten,
-Jeff