Mitsubishi Repair: 91 Galant Tranny issue?, torque convertor, pulse generators

Question
Anthony,  I have a 1991 Mitsu galant with a 2.0 SOHC engine and auto tranny.  First off let me say you was very helpful with a earlier issue with the vehicle and right on the money when you told me to have the TCU checked when the tranny was stuck in 3rd gear.  I got a reman and that corrected the problem.  So thanks again for the help.  Now for the current problem.  Even before the reman TCU was installed the engine would idle very ruff when in drive.  Idle is acceptable in park and reverse and neutral but shakes the car when in drive and sitting still.  It seems to smooth out just as you hit the gas and takes off just fine.  It shifts fine but if you need to stop quickly it will kill the engine 80% of the time.  The ruff idle problem was there before I changed the TCU but I just thought with it being stuck in 3rd gear that was why it idled so ruff.  Now with the good TCU the problem is still there so I proceeded to check other items.  Adjusted TPS and idle and set ignition timing to factory spec.  I checked all internal soleinoids per factory book and all tested good.  Checked pulse generators per factory book and again tested good.  Gave engine a tune up plugs wires cap rotor fuel and air filter.  vacuum checks about 18 and steady. I thought maybe a worn engine or tranny mount bushing was the problem but would not explain why the engine would die if you need to stop quickly.  I am thinking maybe a bad torque convertor but wanted your input before proceeding with this repair.  The tranny history is it was purchased from a salvage yard out of a burned vehicle.  ( burned in the rear) It was a reman tranny I am sure due to the lack of grease build up and the torque convertor was already a reman convertor.  Other than this idle and killing engine issue it drives and shifts just fine.  Thanks Joe.

Answer
Joe,
If your car idles ok in park and neutral when the engine is cold, then that would most likely indicate a intake problem.  This could be due to a dirty throttle body, clogged EGR valve, clogged PCV valve, or a malfunctioning ISC motor.  Cleaning the throttle body and ERG valve are pretty easy, and PCV valves are only a couple bucks and very easy to replace.  Your service manual will outline the procedure to check your ISC motor if you haven't done this already.

But a bad torque converter would also cause the problem you're describing.  And now that your TCU is working properly, you may also want to check your ECU.  I had mentioned in your initial question that Mitsubishi used some unrated capacitors in their car's computers in their early 90's models.  Rough idle, stalling, and eventual inability to start the engine is a sign of this.  You can read this article for further information:
http://www.90gsx.com/eclipse/cap/caps.htm

So if your torque converter checks out ok, it's a good idea to inspect your ECU.  Because eventually, the all these ECU will fail.  Too bad Mitsu never did a recall.
Good luck!