2005 Civic LX Automatic Vibration Mystery
 

I have read that this is a common problem, but I haven't gotten a solid answer on it, or if anyone else has experienced it here...

Vehicle: 2005 Honda Civic LX 4-door, 1.7L, 4-Speed Auto @145K Miles
Problem: Between 35-40 mph, the transmission will shift to 4th and engage the torque converter. The tach reads about 1500-1700 rpm after TC lockup. If light throttle is maintained, a significant, oscillating vibration can be felt from the passenger-front quadrant, near the drivetrain -- and is easily resolved if more throttle is added, or if you back off of it. :confused: This is the only condition and speed at which it occurs and it does not matter about weather, A/C usage, etc. It is the lowest lockup engine speed in the transmission's operating range.

The best way to describe the vibration is a "flappy bumping" -- almost like driving on a washboarded road surface at that precise "wavelength", with that one tire. I would not describe it as lugging. The closest experience I had with it was when packed ice/snow caused a wheel to be out-of-balance and bounced the wheel/tire around -- but this feels more toward the the center of the vehicle by 1/3 (not center, not outboard).

I'm just curious -- it's a close family member's car, and I had just put a new alternator in it and was on the test ride. I thought "Oh @#$%! I've done it now!" When I came back, "Oh yeah, it's been doing that for about 8-9 months now". Whew! :o

Nevertheless, I'm curious about it. I'm trying to help keep this car on the road as long as possible.

RH77

Update:

I drove it outside of rush-hour traffic today to gather more info...

If the throttle condition was maintained during the oscillation, it wildly increased in amplitude until my concerns for the components forced backing-off.

It's not a "vibration" -- that's too fast. Picture a ceiling fan out of balance -- or a sine-wave oscillation.

I'm trying to learn to self-maintain vehicles as best as possible, and as safe as possible. Something is clearly amiss when the drivetrain accepts torque at the lowest RPM allowed by the ECU/TCU.

Thanks in advance for any clues!

-Rick / RH77