I recall a story a buddy of mine told me a few years back.
It was of a woman whos MB wouldn't run right for quite some time. After much frustration he finally replaced the non OE wires with a factory set (wasn't cheap). This instantly solved the problem. Apparently the aftermarket wires had a different resistance or improper shielding. From what I understand "Crosstalk" or Noise can confuse the electronics in the car.
Also, make sure the wires are going to the proper cylinder. Sounds simple but it happened to me once.