Yeah, mine would blip-whistle a few times at normal op temps at stoplights. Engine would rev up and down a little, but it did this for probably 90k miles with no other problems caused. I sold it as-is. I think the part is several hundred $$$

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL