Hi folks. I have a 1993 W140 with the M104 engine. When the engine reaches the rpm for the cam advance magnet to be energized, I get a loud rattle, almost like when a lifter sticks (like marbles in a can). When I lift off the throttle, the noise goes away. I unplugged the cam advance magnet and the noise goes away. I also have poor idle and a running rich condition (however, this may be due to a bad O2 sensor...I am getting a code 22 on pin 4 (02 sensor heater open/short circuit) along with a code 24 (left camshaft solenoid open or short circuit) on pin 4 (38 pin test port)). I believe code 24 is because the fuse was blown for this circuit on the CAN BUS module. I tested again after I replaced the fuse and still get the same code, which is confusing because there is power going to the cam magnet. I have driven the car a couple of days and need to retest to see if the code is still there. Bottom line, plugged in it the noise appears when the cam magnet operates (around 1,500 rpm under load, and 3,000 rpm when the engine is revved at idle, which is correct), and when unplugged, there is no noise, the car idles rough but drives smooth, although sluggish, obviously.

I've replaced the plugs, wires, cap, rotor and coil, and I replaced the cam magnet solenoid.

Any ideas on what's causing this noise? I don't believe I have a timing chain issue. The car runs fine (other than being a little sluggish due to no advanced timing, and the rough idle problem) and drives very smooth down the road.

I'm really at a loss as to what to check or how to diagnose. I thought about pulling the cam magnet off of the car, starting the car and manually pulling the cam sleeve that the magnet would normally pull forward to see if the noise presents itself. I believe this sleeve is pulled to allow oil flow to change, advancing the left camshaft.

Finally, the only other thing I can think of is replacing the cam position sensor on the side of the head as I have read this can affect how the ECM causes the cam magnet to operate. I've always though the cam position sensor either works or doesn't with no in between, but I had a Ford Ranger act up where it would cut out under heavy load and it was the CPS. I hate to keep throwing money and parts to a car but I'm completely at a loss.

I hope someone else has an idea! I've posted on two other MB forums with no response at all.

Thanks!