This might be too simple but I had a shaking problem at idle, at first not too bad then after the car warmed up it seemed to shake more. I lifted the hood and noticed bubbles in my primary filter. Replaced the fuel line leading up to the primary filter (the clear inline filter) and cleared the problem right up. The fuel line was old and cracked right under the hose clamp.
Hope this helps.

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83 TD wagon "Madge" PO's given name. 410k (150k engine)