I reside in Nigeria, and I have this used Mercedes 190E 2.3 1992 W102-numbered engine that I bought 3 years ago. The same year I bought it, the mechanic changed what he calls the Injector switch, which he told me coordinates the supply of fuel to the injector. This was after I experienced car-start difficulties. I honestly dont know much about these things, but after he changed the part, the car behaved normally.
Lately, I noticed that the car starts sluggishly, whether cold or hot. I also here a tapping sound whenever I idle the engine after a cold start. The mechanic says once again that its the same black injector switch that is causing the problem.
I want to know more about the car hence this post. I hope someone here can help me. Please let me know if I have supplied enough info for a diagnosis.

Thanks.