1999 Ford Escort car idles up & down, high & low

I just bought this car used. It idles high and low and up and down when I am driving. It happens especially bad when I hit the brakes to slow down or come to a stop. It shakes like it wants to stall out. If I put it in park and rev the engine it doesn't stall. It was recommended to me to replace the idle control valve but I live in Germany and will have to pay alot of $ to get any repairs done so I want to be sure before I order any parts. Should I wait on the idle control valve until I replace plugs, wires, fuel filter, oil filter, etc?