Originally Posted by
mobilefitt
More news. It appears like an intermittent vibration that I thought was in my drive line, may have in-fact been the engine vibrating. The vac tube in the front of the motor apparently opens and closes valve flaps in the manifold. It is my theory that these flaps have been fluttering at cruise speed. I've been chasing this vibration since I started driving the car. Thrumming, oscillating , rhythmic in 6th gear at about 65 mph to 70. The trick is it doesn't happen every time but when it does, it's always the same. No matter what speed, you can set your watch by the rhythm so I concluded it wasn't wheels/tires.
My next best culprit would be the flex disks & drive train support. I have it in my cart from rock auto and the car has completely stopped doing it since the vac tube repair????
I hope it stays away! I will prob still update the drive train parts as well.
Sounds perfectly feasible, You have a manual, correct? IF it does happen again, not what speed and RPM. If say 67mph in 6th gear, set the cruise while it is happening, and drop to 5th. If you are correct about the engine itself being the cause, it should go away or change at the higher RPM.
Or say 67 in 6th is 2200 RPM (just guessing), put it in 5th and drive 2200 RPM (55ish?) and see if it happens.