The signature C36 fault is the M104's biodegradable wiring insulation, which breaks down and causes random electrical gremlins; owners consider a documented harness replacement a major value-add. The problem was resolved for the 1997 model year, and the engine harnesses are year-specific and non-interchangeable.
M104 engine wiring harness biodegradation (C36)
Mercedes-Benz C36/C43 AMG (W202) · mechanical