Idle vibration?

[944lvr]

I have an mint 87 944 na with an automatic lately I've noticed that when i hold down the brake while im stuck at a light the car vibrates like crazy but when i let go the vibration stops. if anyone can help me with this problem I'd really appreciate it.

[Pilot_951S]

Sounds like either a motor mount a tranny mount, or a faulty idle control valve. If it's the ICV then what you should notice is very LOW RPMs when teh car is in gear and you are stopped with your foot on eth brake, like less than 800rpm. That however is a long shot, its probably a mount

[Cebu]

I had the same problem(86 944na A/T).The transmission mount, top aft center of transmission is loose/broken or bolt has come out.Look to see if the drive train torque tube shield is resting on the rear suspension torsion bar housing(center aft).Jack tranny up and insert a thick rubber pad(I used two brake pedal pads), operate vehicle to see if vibration has gone away. This will probably isolate the cause.

[TomH]

One other thought. How do you know when the AT Flex Disc has gone bad. My guess is the trans will vibrate at all RPMs. I, too, have an AT, so that's why I'm curious about this overly expensive part

[Ven]

My 85 had the same problem. I went to look at the idle control valve but first I looked in my throtle body and it was filthy! I shot some carb cleaner in in and whola problem gone. But I woul have to guess the valve is junked up as well seing after seeing how dirty the throtle body was. It might have something to do with my sudden loss of RPM's when I let of the accelerator, It gently looses RPM's until 2K then drops 300 RPM's for no reason.