I've had 4 separate instances of rough running that were corrected with a coil swap. In all 4 cases, no codes were present. Is it possible for a coil to be "weak" enough to cause run problems, but not weak enough to trip a fault code? Are there certain types of coil failures that don't trip fault codes?

As a side note, the coil to plug "boot" type connectors are also a known common failure item. They are cheap enough that I replace them any time I have run problems, change plugs, etc......

J. M. van Swaay

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1994 E320 Wagon, 230,000 miles
1995 E320 Sedan, 106,000 miles
1994 E500 Sedan, 79,000 miles