XJguy

Ive checked all the codes (none), tensioners look fine, car runs great. RPMs are good, oil pressure good, power good, car starts up with no problems, has new harness, new motor mount, all fluids changed at regular intervals. But when in gear, and stopped there is a rattle coming from what seems to be the upper right of the engine, It seems to be coming from the valve train. I've used a mechanic's stethoscope and from what I can tell the noise is coming from the top right (if you are looking at the engine) front of the engine. Another thing that happens is that when in gear and stopped the idle is a little lumpy, causes a noticeable vibration in the car, and a annoying sub-bass sound, not quiet and smooth. I have been racking my brains and looking everywhere as to what it might be. The car has 122k miles and has Mobile 1 oil and only premium fuel. At idle and in Park its normal, smooth as it should be and acceleration and performance is great as well.

Can it be worn valvetrain? Timing chain? Timing chain guide? Camshaft adjuster?

Plutoe

could be a sticky valve!!

XJguy

Wouldn't a sticky valve cause running problems or noise when accelerating?

BeachFreak

Try taking the serpentine belt off to see if the noise goes away. If not, then you are definitely narrowing it down to the tensioner, or valves, something inside the motor.

XJguy

Okay, so today I dive in, and I am happy to say that the rattles are all coming from the belt tensioner shock, specifically the upper bushing. But it turns out its quite a task to replace. I bought a new shock, and will replace it eventually but for now I am happy that I know its not the head and the engine isn't about to go. I suspect the vibrations I am feeling while in gear are also because of this thing. Ill know for sure when I replace it.

BeachFreak

Lucky you... that's what I had hoped was my problem. Instead, I am stuck and unable to get the bolts loose on my water pump. Power steering pump and tensioner out of the way, but I can't get any further.

XJguy

Okay so here is an update on all my W124 M104 woes. Some of you called it correctly right off the bat.

The hard start was due to a faulty (leaking) fuel pressure regulator.

The rattle noise was due to a bad belt tensioner shock bushing.

The reason why I noticed the bad shock bushing was due to a bad passenger side engine mount causing vibrations....which visually looked fine, until it finally ruptured spilling its oily guts.


Thanks all hope this info helps someone else.