My car runs well most of the time, but it once in a rare while, upon cold starts, stalls when put into drive. Also, maybe related or unrelated, the econ gauge goes to approximately 1/4 of the way down at idle and with the a/c on, it goes almost to 1/2, would this indicate a vacuum leak or what should I look for? Also, how much would this affect performance or economy? The transmission also shifts slightly harsh, I presume from the vacuum issue.

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currently just 1989 300SE 185k miles