Based on the advice of this and one other threads, I asked MB to replace the wiring harness to correct the "check Engine light" and code 19. The 94 E420 had nearly 95,000 miles on it at the time. Mercedes approved it under the secret warranty and it was replaced for free. It solved everything. The car does not record any check engine codes anymore, and the car has never ran so well since I purchased it at 5 years old. I guess it has been a problem all along. MB had thought I needed a new computer at one point, but the wiring harness replacement has solved that also. The car now has 115,000 miles on it.

If you are having any troubles with your 94 E420, don't hesitate to enact this secret warranty.