We just purchased a 91 Ext E4WD, automatic w/4.0. It has an intermitent vibration, though vibration is really to gentle a word for it. It is not speed related, but is related to load. And when it happens, it happens only under specific circumstances. If youa re dirving dow the freeway and you completely let off the gas and then gently apply the gas again, theengine will run for a while and then slowdown (fixed throttle and roadspeed) almost as if it were upshifting into OD. BUt it is not going into OD. I believe what it is doing may be locking up the torque converter. For simplicity's sake, lets say that what is happening. Then assuming that, it only vibrates when the TC is locked. Give a stab on the throttle or let off th throttle and then get back on it and the vibration goes away, until the TC locks up again (or whatever is really happening if it isn't the TC). It shakes the dickens out of the whole van, and short of causing it to shift gears or unlock the TC, throttle position does not affect it, other than to make it worse as the load on the drivetrain increases.

Any ideas, suggestions. Is it the TC, or maybe the E4WD? It feels like it is in the front of the car. I am pretty sure it is not an OD issue because I get it even with the trans in D rather than OD.

 

I fear you may have a failing torque converter. What does that tach do during this time?

 

Does not have a tach, but engine speed does not sound like it is changing at all.

 

You may want to post this in the transmission forum, perhaps you can get someone else who has had this experience.