This is what solved a simliar 20 minute stall and no start problem on a 1993 LS400 that I was working on.
Found all the info about bad capactors in the ECU, found some leakage and decided to replace the capacitors and hoped this soled my problems. It did not solve the problems.
Then I moved on and reinspected the ECU VERY carefully. I found 1 surface mount resistor that appeared to be discolored and like it had leakage a bad capacitor, but it did not have any capacitor near or above it.
Brushed this resistor off very well. Had to get the silicon sealer off of the component. Turns out the sealer had bubbled and become warm. Close inspection indicated tha the resistor had a cracked/cold solder joint. Reflowed the resistor and cross my fingers.
Forgot to take pictures or get the exact resistor component number. It was a 200 series resistor R2XX. Located in line with the E9 ECU connector. The resistor was next to the 2nd vertically mounted transistor array that was about 1 1/4" wide by 3/16" thick.
Short story, the problem was with the cold/cracked resistor solder joint. Car would run about 20 minutes, then die. No tach when cranking, but the engine would run on brake cleaner.
Resoldering the bad resistor solder joint, priceless!
