TomO:

Your problem is the same as mine. I already fixed the problem. After washing my car's engine, a week later the car started to have stumble idle and it was intermittent. The malfunction light never come on. Ater the problem started, I replaced spark plugs, fuel filter, clean fuel injectors. The problem was still there. When I replaced the spark plugs, I noticed that the spark plug in cylinder #6 was orange. Water got into the spark plug well when I washed the engine. Because I parked the car on the slope driveway, water was geting to the spark plug well #6. Since you did replace the ignition coil boot and spark plugs, I would check to make sure that the replaced spark plug is not a resistant ones. Measure the spark plug resistant, make sure they are not high resistant spark plug (use Bosch copper spark plug only). Next, I would measure the resistant of the spark plug wires to make sure that they are about 2 kohm as specified by MB and have no crack on the insulation. Then I would took the ignition coils out and measure the primary resistance and the secondary resistance of the coils. The primary side of the coil between the connector terminals (12 V input wire) . The secondary side is between the connector of the boots to the connector of the spark plug wire. The primary side should be about 0.7 ohm and the secondary side should be around 6.7 kohm. Measure the three coils to see if they are consistent. This will help you to identify if the coils or the spark plug wires cause problem. Good luck