ytech15, the 104 engine in our 1992 300CE had a disconcerting, abnormal noise at idle. A local indie told me not to worry about the noise; however, an experienced tech at our local MB dealer diagnosed the problem as a failing timing chain tensioner. A new timing chain tensioner (installed at the dealership) resolved the problem. As far replacing the tensioner yourself, it's critical to maintain the timing marks with the camshaft. If you decide on DIY, be sure to have detailed MB instructions that you follow exactly. Otherwise you could end up destroying the engine. I doubt that your timing chain would need replacement, but you should check for any stretch. Typically the timing chain guides need replacement on older, high mileage engines.

Mobil 1, as well as other high quality, oil has additives that keep the engine clean. As you probably realize, hydraulic lifters rely on oil pressure to keep them tight against the camshaft so they are quiet. Routine oil and filter changes with a high quality oil will extend engine life. If your engine has been neglected, it's possible you need to replace the hydraulic lifters. I have put 200,000 miles on a 104 engine without the need for any major engine work.

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Fred Hoelzle