Mitsubishi Repair: Dies when put in gear., air intake hose, neutral safety switch

Question
Hi, question for you we have a 1990 Mitsubishi Montero RS Automatic.

And for the past couple of days we have been trying to get it started, and stay running in gear.  Yesterday we replaced the battery because it only started with a booster-pack connected to the battery.  We were trying different things and I was in side holding the key in the START and my friend Allen was moving the connecters of the booster-pack too see if we could possible get a better connection.  I was getting bored a started looking at different things and I grabed the gear selector and moved it and the second I moved the selector the engine cranked over great.  At the same time we were in the process of checking the engine compression and it read 119 psi, specs say 119 psi.  

   So I got to thinking and moved the gear slector again and moved the key in the START position and nothing happened and we tried it over and over again.  So Allen was looking at it and put it into neutral and moved the key to the START position and it started, he did this a couple of times.  Every time it started fine, moved it to park nothing happened.  So we replaced the Park-Neutral Safety Switch, and it started like normal in park a nd neutral.  We started cleaning up and went to pull the Montero out and it died when we put it into reverse.  We put it in to neutral started it and put it into drive it died.  Put it in Park started it and moved it to Neutral it died.  While testing different parts, we took off the air intake hose, and Idle Air Control and cleaned them both.  Allen was trying different ideas and started it in Neutral reaved the RPM up and held the RPM were it was and pushed the brake pedal and put it into Drive, held the RPM were it was for a few seconds and let the brake goe a it drove fine.  We pulled it out last night and left it.  This morning Allen went out and started it and put it into drive and it drove like it had no problems at all.  Shut it off and went got his tools ready.  Started doing different things on it and started it and three seconds later it dies.  Put it into gear and it dies.  Allen tried starting over and over same thing any help will be great.

Craig Gallup
208-745-7704
attn.  Auto Shop.

Answer
Craig,
You should pull and inspect the car's ECU and TCU.  There is a know issue with the capacitors used in Mitsubishi computers.  You can read this article for further information:
http://www.90gsx.com/eclipse/cap/caps.htm

If you see damage to either of these units, they'll need to be replaced.  You can even send the ECU and/or TCU out to have it tested.  You may have luck finding a used ECU or TCU at a local salvage yard or on eBay.
Good luck!