My 86' 190e had a used engine put in it that has around 80,000 miles on it. Recently, it has started idling rough upon starting and hesitates for about a half mile, then smoothes out and runs well. I know that the overvoltage relay can cause these problems but it's fine and it starts and idles fine when the engine has been running. I live in Tennessee, so the weather has stayed fairly warm and I'm worried about how long it might take in the winter to idle smooth. I was also wondering what kind of damage could be done to the combustion chamber when part of the porcelin that surrounds the electrode falls into the engine. I found that one of my Bosch super's had done this when trying to remedy this idle problem. Thank you.

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86 190E 8v 200,000 mi.