Did you check your O2 sensor?
Did you check your EHA current with the test harness from Mercedes?
Did you check your duty cycle reading from the X11 connector?
Do a search on all the above here on this forum.
The 190E 2.3 engine is about 99% similar to your 230CE so do a search and you should find some good tests that you should be able to do on your own. You will understand a lot about yor car