97 E420 119 engine, 105k miles

problems:
1. at idle or moving, there is a tapping/ticking noise that seems to be coming from the lower half of the engine (rod bearing?). happens at P, N or D. The tapping gets quicker when I shift to N/D than at P, and the frequency increases as I give more gas. What is the problem and how urgently should this be addressed?

2. Car has a rough idle (at D or P, but worse in D). At P rpm is a bit higher but at D when the rpm is at about 700, the rpm would drop to 400-500 and then the car would get it up to 700 again.. this happens every 15-20 seconds. Car doesn't die though. No engine malfunction codes.

Are you the same guy that just had the timing chain replaced?

no.

Oh, ok , someone just called me with those similar problems on a 97 e-420 that just had a timing chain replaced and oiler tubes replaced due to engine ticking.
I was just wondering why those important details may have been left out.

Those 119 engines are notorious for having the plastic oiler tubes blow out inside the valve cover.

Question: Did the ticking noise and the rough idle happen simultaneously or one before the other?

You may or may not have more than one problem.

i've had the car for only 2 days so i can't say for sure when they started. possibly a while ago.

i was browsing another thread and found some interesting info. this gentleman had a very similar tapping noise, but check out his solution:

"
Turns out the problem was related to a Tech Service Bulletin P-B-07,00/21F-1260. They replaced front engine mounts with an updated mount. It completely quieted the engine ticking noise.

"