* Problem with the check engine MIL is that it could be on for any of a number of things. Good news is that they are all emissions-related and don't portend some engine disaster.
* Give yourself any help you can by first checking for fault codes (at the rectangular data plug). Also check for on-off ratio faults (at the circular plug). Popular culprits are oxygen sensor, EGR malfunction, coolant temp sensor. Don't think that problems like a leaking fuel-evap system or a damaged catalytic converter will turn the light on in a '93 190E.
* Have read posts on this forum about getting the fault codes scanned at one of the parts stores if you don't have a scanner (maybe Autozone or Autowize?). Note that your car doesn't have an OBD data plug.