How can I test my torque converter to determine.

If the drive shaft is out of balance or the angles of the u-joints is incorrect due to weak springs or more commonly altering the carefully-designed ride height, your dentures will vibrate out!

The most common cause of a failed torque converter is a failure of the clutch to lock up, or it may shudder. (Be aware too that the wrong transmission fluid will cause a shudder). With the engine warmed up, accelerate gradually up to highway speed and keep an eye on the tach. You'll feel the shifts to second, third, and overdrive, plus you should feel the lockup occur. That will be in third or overdrive and you'll see about a 200 rpm drop. Once that has occurred, press the accelerator pedal a half inch to accelerate perhaps another ten miles per hour. The tach should not increase suddenly. It will creep up slowly along with vehicle speed.

Next, hold the gas pedal perfectly steady and briefly tap the brake pedal with your left foot. You will see the engine speed go up 200 rpm, then drop back down a few seconds later when the torque converter relocks. It unlocked in preparation for coming to a stop. It will also unlock as you approach wide-open-throttle or if you just accelerate quickly. If you feel a shudder for one or two seconds each time it locks up, start with a fluid and filter change.

If you feel that shudder and / or you notice that 200 rpm increase while you're cruising at a steady highway speed, suspect the throttle position sensor. The lockup feature was first developed by Chrysler and used on some '76 or '77 models and they were hydraulically-controlled. Yours is electrically-controlled. The throttle position sensor is one of the things the computer looks at to determine when lockup is appropriate. Normally a dropout in signal voltage will set a fault code and turn on the Check Engine light, but if the dropout is too short, there may be no code set but you will have intermittent unlocking. That seems to be much more common with diesel engines.

Carefully stuff it in neutral, turn off the engine, and cost, then see if the vibration is still there. If it's related to the torque converter, even just letting the engine idle will make it go away but you'll have to be in neutral.

The automatic idle speed motor, (idle air control) only affects idle speed; nothing else.

Most logically any shaking is due to something rotating that is out-of-balance and you need to make things rotate at different speeds to isolate the suspects. By shifting to neutral and allowing the engine to stall or idle, the outer half of the torque converter will be rotating at idle speed along with the engine. In neutral, all of the internal parts of the transmission along with the inner part of the torque converter will essentially stop rotating. If you still feel the vibration, it's not those parts.

The most likely suspects are the universal joints. One definite clue is a metallic banging every time you shift between drive and reverse. The less obvious clue is rust around one of the bearing cups. Typically that shows up when one of those cups is tight and binding. You have to remove the drive shaft to feel those. A tight bearing cup prevents the joint from swiveling smoothly in all directions.