I am glad that the rack dampener was suggested, that is what I would assume is the problem. Do a search on Rack dampener, because you will find many posts about adjusting it properly.

The key is to back it out all the way, after loosening the outer locknut. Turn it in until it just touches the rack. With the car running, rev the engine with the stop lever, and listen for a dead spot at the end of acceleration. If you hear a dead spot, turn the adjusting bolt in 1/4 of a turn, rev it again, etc., etc.. You will know when it is adjusted correctly, because your engine will not die, or idle irregularly when you come to a stop. I fiddled with mine for several weeks until it was perfect. I kept the two different wrenches in the car, and every time I drove somewhere, I turned it a little further in until the idle was perfect. It is sometimes hard to do without driving it between adjustments.

Congratulations on your Wagon!