Smoke on start-up is a classic symptom of worn valve guides / stem seals.

Next stage in the progression is for it to smoke badly when you drive off again after coasting to a stop.

If it's only on start-up, you can probably drive like that for a long time.

I agree that checking the modulator is a good move, although a modulator would usually smoke at idle even when warm, and you'd notice a pretty heavy ATF consumption.

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1987 W201 190D