I have an 87 Honda Prelude with auto, 1.8L SOHC Dual Carb, completely stock with 142,000 miles. I've had it for a couple of years and put about 30,000 miles on it. It's always been rather loud at high speed, but now it's become bumpy as hell and causes major vibrations in the whole car. I think there might be something wrong with the engine because tonight I got it up to about 90, stuck it in neutral, and it was smooth as silk. I had thought maybe the tires were out of balance or something, but since it runs fine in neutral I'm really worried now. This problem is less noticeable downhill or any time the engine is operating under low throttle. Again, it's most noticeable in overdrive going uphill at speeds in excess of 80 mph. Any ideas? I've been reading posts on this website for about a year, and I feel like I've really learned a lot here. Thanks for educating me about Hondas and cars in general!