When you pull the OVP Relay does the idle change? Have you checked your plugs, wires, cap and rotor? When was the last time they were change? Next test you O2 sensor as well. I am betting the OVP is bad since you said it rattles. I have two and neither ratter or make any sound when shaken.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....