1995 S500 check engine light on.

Check for vacuum leaks. Make sure that all of the spark plug wires are attached. Be sure that the air filter and all of the hoses are on tight. It's probably something like that. To clear the CEL. Disconnect the battery for about a half hour.

I would get a code reader and scan to see what code tripped the check engine light, repair and then reset the CEL light. Whatever tripped the light is probly connected to the engine running rough. Also if what to check the codes for free your local parts store should be able to do this for you. I would not advise disconneting the battery since it might cause you to lose the security code for your radio and may affect other electronic functions.

if you don't have access to an analyzer and you've done all of the above and the light still comes back, check your coils, change wires, the spark plugs and the fuel filter, I suggest to clean your fuel injectors. Getting the codes will make your life easier.

Thank you all for your help. I took my car to a Meecedes specialist, not a dealer. They found 3 codes: throttle body, air mass meter and air injection faulty code. They check the air pump, it's working. They can't find the exact problem and have to charge me more for further test. Your help is very appreciated. Kals

good luck

Replace the Mass Air Sensor

Try to find one for a 1995