1997 Chrysler Town and Country Engine starts, but won't con

This is an intermittant problem/condition !

Engine starts, but will not run. Immediately dies after about 1 - 2 second delay. When its in this "mood/cycle, " it will not start. When its in the "other mood" it will immediately start, run, and operate normally. So far, it has never died while moving under power.

Vehicle was towed to dealer who had suggestions, but could not find any "codes" and would not insure their significantly expensive solution would work. Car later started (next day) and ran fine. They offered no explaination. Drove it to a mechanic who replaced the oil pressure / sender unit, oil change, and other regular maintenance. He drove the van back and forth to his home over 2-3 days with his computer connected -- with no codes.

Back home and several days later, upon repeating the same problem (cranks fine, starts, and immediately dies with the check engine/no oil light on), I noted that the RPMs are zero/do not move duruing the crank and start. Later on, when its operating normally, RPM gage works fine. While in the won't start/run mood, I opened the door to exit the vehicle and tried to start again and it started. (I also had banged my fist on the dash ONE time -- medium blow -- thus, I'm thinking there is a short circuit under the dash.

Ideas?