From what you describe, azari, it sound like you got a valve lifter that doesn't do its job very well. The sound is because it looses oil pressure and a clearance between valve and lifter occur. If this is the case you have got hydralic "selfadjusting" lifters.
16 valve engines came with mechanical adjusted lifters
One thing you could try is to change oil if not done recently, and make sure you use one that is within specs for the engine. You will find this information in your manual.
If one/several lifters gone bad you got to options:
1. Have a trained mech to look at it. He can determine if it need to be adjusted or replaced (this is said to be a non-DIY)
2. Change the bad one...
'87 MBenz 190E 2,3 8vlv