Oldsmobile/Buick Repair: Buick Vibrations, accelerator pedal, buick lesabre

Question
Van,

I own (regretfully) a 1996 Buick LeSabre.  I have a slight vibration that is felt through the accelerator pedal at about 1500 rpm but when I accelerate(>1800rpm) or decelerate (<1200rpm) the vibration goes away.  When I turn the AC off the vibration immediately goes away.  The AC appears to be working just fine and I have had the Alternator checked and it appears to be working fine to (it is correctly charging at least).  I thought it might be the bearings in the alternator but it seems odd that the vibration would go away with the exception of the 1500 rpm range.  Other repairs made to the car was a new water pump back in December...the vibration started about 1 month ago.  

Answer
Hello Richard,
The accelerator is connected under the hood to the throttle body with a cable and housing I believe.
Look at that cable, and see if there is a hose or somethind laying against it that might be transmitting the vibration.
Check the a/c compressor to see if it happens to be a little loose where it mounts.

Another thing to do is have someone hold the gas pedal at the engine speed where it vibrates, and look at the serpentine belt, fan, etc, and see if you can see anything vibrating about the same frequency.

Van