Strange vibrations...

[liju@travelin.com]

It all started late yesterday afternoon. I was driving back from grocery 
shopping (sorry about all the details) when I noticed that every time let off 
the throttle there was a vibrating noise that seemed to be coming from near the 
shifter or in the vicinity of:. I shut off all the gadgets and listened more 
closely. The car ran normally as long as I had my foot on the throttle. Odd.

So I continue on till I got off the highway when I noticed that as I downshifted 
there was much more pronounced vibration from the same area. It seemed to 
"shudder" more as I applied the brakes and came to a stop. When I start to move 
again there's the "shudder" for a few seconds and then the car drives normally 
again. When i got home I checked as many things as my knowledge of the car 
permitted me to. I took the car to my mechanic at around 5.15 or so. He put it 
up on the lift. No signs of anything loose or broken (I thougt the drive shaft 
might be loose or something? maybe the universal joint?) He did notice that 
there was some hydraulic fluid leaking from the steering rack. Nothing 
conclusive and I test drive was any help either because all the symptoms had 
disappeared!

I promised to bring back the car next week for a closer look and then left. Sure 
enough when I about half way home...the shudder, the vibrating noise that sounds 
like the drive shaft might be loose...were all back. This morning I checked 
fluid levels and the hydraulic was low; so I topped it off. For a moment I 
thiought everything was okay but all the vibrations were still there. The 
hydaulic fluid level is normal for now. i am extremely anxious about what it 
might be and there are no professionals open during the holidays so I'm stuck.
I would more than appreciate any and all thoughts on what it might be. I suspect 
the power steering rack($$) and the transmission (still more $$$) only because 
the car drives normally under accelaration and throttle). Incedently what should 
an 87 5kTq idle at? Right now it idles at about 1100 rpm and 3.0 to 4.0 lbs of 
pressure. TIA.

Liju.  875kTq.