Engine light come on often and goes out on 2000 Mercedes-Benz E430

Why does the engine light come on and go off?

2 answers
It is a warning light that is illuminated when there is a problem with the EMISSION SYSTEM only. Emission system being the pollution control system.
This can happen for a number of reasons. Check out the RepairPal article on the check engine light: http://repairpal.com/check-engine-light and also the common problems page for your car: http://repairpal.com/mercedes-benz-e430-2000/common_problems

You may find what you need there.