My car idles about 400 rpm less when the engine is cold compared to when it is warm. It did not use to be that much different but now it is and when you adjust the idle with the engine is warm then when it is cold it is way to low and engine virbrates the air filter housing to much. What causes this would a new syle rack damper bolt cure this problem ?

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84 300 Turbo / 320,000
96 E300 D / 55,000