[Corndonkey]

I have a 2008 328xi that over the past year has started having what feels like misfire and engine stumbling once the car is warmed up and I'm driving. The idle is rock solid with no issues. Once I start accelerating, it has this sort of hiccup, where you can feel the car misfire every now and then. I can only describe it as sounding like this:
"ehhhhhhhhhhhh-HEH-ehhhh-HEH-ehhhhhhhhhhh-HEH-HEH-ehhhhhh"

IT's not consistent, and is worse when the coils are under load (low RPMs but going up hill, say). I've replaced the coils, the spark plugs, the VANOS solenoids and the fuel injectors, with absolutely no effect.

I THINK there's a loose connection/ground in the wiring harness - if this were an old car with central ignition coil, i'd next change the plug wires, but since the coils are at the plugs, that's not as easy to do.

Any thoughts? Anyone else have this problem? I've been searching on and off over the past year for help, but can't find the same issue.

Also, how best to test the conductivity of the individual wiring harness wires to/from the coils? I think that's my next step, but can't find where the harness connections are for each individual coil in the j-box at the rear/passenger side of the engine space.

Any help would be GREATLY appreciated!