What could be causing this "washboard" effect in my Tercel?

Dear Car Talk

Dear Car Talk | May 01, 1995

Dear Tom and Ray:

Our 1987 Toyota Tercel has a peculiar problem that we haven't been able to demonstrate for our Toyota dealer or our local mechanic. When the car has been out in the rain overnight, parked on the street as usual, after starting it, there will be a "washboard" type of effect felt and heard upon acceleration. This effect will go on and off at about three or four second intervals for about 45 seconds, and then disappear. The sound is not real loud, nor is the feeling very shocking, but it's there. Our mechanics can't duplicate the conditions at the shop, because the cars are kept inside overnight for insurance purposes. Can you help?

TOM: I'm confused by your use of the term "washboard," Ron.

RAY: That's because he never washes his clothes. He just drives through the car wash with the top down on his '63 Dart.

TOM: No. It's because "washboard" usually describes some sort of severe ride problem. What you're describing sounds more like a cylinder that's intermittently not firing.

RAY: That could cause intermittent stuttering or bucking on acceleration, which would be subtle, but you could definitely feel a "jerking", and hear the change in engine sound. I'm going to have to assume that's what you mean by a "washboard" effect.

TOM: In which case I'd look at the ignition system. A faulty distributor cap, rotor, spark plug wire, or any other part of the electronic ignition system could easily be affected by rain, and could cause this kind of misfiring.

RAY: You're going to have to get your mechanic to experience this. Even though he can't leave your car out in the rain overnight at the garage, that doesn't mean YOU can't. So park your car out on the street near the garage next time it rains, and get a ride over there first thing in the morning. Then take "Gus" for a ride and let him experience the problem first hand.

TOM: And if the car happens to get stolen overnight, chances are your next Tercel won't have this problem.

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