96 Vibration at idle

I am getting a kind of silent but buzzing vibration thru the wheel and dashboard when waiting at a traffic light that goes away when accelerating, just happens when at a complete stop in Drive (96 Caprice 4.3L). I noticed it the most when changing radio stations, because the buttons on the radio are all vibrating, as is the rest of the dash, a little less thru the steering wheel.
Strange part is, it seems to happen the AC is on, but when you shut off the AC it continues to vibrate at traffic lights until the next time you shut the car off, then the next drive will be vibration-free until the AC is turned on, etc.
It is a kind of intermittent buzzing vibration (no noise, just vibration), sometimes like buzzzz, stop, buzzzz, stop, etc., sometimes goes up and down with the turn signals too, always at a stop in D.
Anyone else have this problem?

What is the idle RPM when this occurs? You may have to connect diagnostic equipment to monitor that. If the engine RPM drops below the target idle ± 50 RPM there may be vibration induced by the power steering pump, transmission oil pump, AC compressor, and from the engine mechanicals such as individual cylinder firings and valve train.

If the engine RPM is near target, it may be helpful to check the harmonic damper on the front of the crank for damage.

I don't know what the RPM is, I don't have a tachometer. There really isn't anything else obviously wrong, no check engine light or anything like that, just vibrates at idle. Like I mentioned the most unusual thing is that is starts when you put the AC on, but keeps vibrating after you shut the a/c off, and only stops when the car is shut off and restarted without the ac on. Is there anything that would go on with the AC and keep going even after it's shut off? I checked the electric fan in front and 1 out of the 2 was going, not sure if the other one is supp. to be on as well.

I am getting a kind of silent but buzzing vibration thru the wheel and dashboard when waiting at a traffic light that goes away when accelerating, just happens when at a complete stop in Drive (96 Caprice 4.3L). I noticed it the most when changing radio stations, because the buttons on the radio are all vibrating, as is the rest of the dash, a little less thru the steering wheel.
Strange part is, it seems to happen the AC is on, but when you shut off the AC it continues to vibrate at traffic lights until the next time you shut the car off, then the next drive will be vibration-free until the AC is turned on, etc.
It is a kind of intermittent buzzing vibration (no noise, just vibration), sometimes like buzzzz, stop, buzzzz, stop, etc., sometimes goes up and down with the turn signals too, always at a stop in D.
Anyone else have this problem?


before getting into complex troubleshooting check for vacuum leaks,,,pcv hoses and even replace the pcv...at this age these hoses split esp. at the 90deg bend points..

idle issues are most often in this area....

could be the engine/hvac condenser cooling fans....bearings/blades damaged dirty...

Is there a vacuum diagram somewhere on the web that shows where all of the vac. lines are located? Doesn't sound like a bad idea to check all of them.