My '92 740 (non-turbo) with Rex-Regina runs fantastic when the outside temp is 60 degrees F or higher. But below that temp, the engine vibration gets progressively worse. When it's 20 degrees F, the vibration is deafening, particularly at idle.

It seems to have nothing to do with ENGINE temperature. Even when the car is fully warmed up, in colder weather, the vibes are MUCH louder.

In recent months, I have cleaned the throttle body and idle speed motor, and replaced the following:

Air Temp Sensor
MAP Sensor
Plug wires, Distributor Cap and Rotor
Fuel Filter

I didn't think the coolant temp sensor would be causing it because the problem seems so connected to outside temp. WHAT is causing these drastically louder engine vibrations in cold weather? The car is otherwise fine. Always starts, no warning lights, good gas mileage, consistent idle.

Thanks to everyone, and Happy Holidays!
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Guid ('92 745 257k, '91 940 SE 278k,)