Yep, my '86 has been doing the same thing for the last couple of years now. It freaked me out when it first started doing it because I saw, or thought I saw, it out of the corner of my eye. After a couple of months, I would catch it jumping while I was at a stop or near stopped up to 35 to 40 mph. No alot of people had the same effect, but now I'm used to it. Its just another little quirk in my ride. It doesn't happen all the time either, just about 20% of the time.
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'86 sedan with 407,000 miles on the original engine and automatic transmission