I've done a little bit of custom electronics design on my NSX for light controls, and discovered connectors that slide together nicely, but had occasionally had an individual pin that was loose. A careful tightening with small pliers was the fix.
With you replacing the EPS rack itself and the control module itself, that leaves other devices (sensors) and the wiring. For the wiring, a "wit's end" thing to try: get individual male and female connector pins (ie, no connector body) for each type of connector used. I got mine via a local junk yard that let me cut the connectors off of a wrecked Civic.
1. Slide the test pins on & off of each wire in the connectors. See if the pins slide on smoothly with a tiny bit of pressure, but without any wobble or looseness.
2. Check end to end connections through the wiring harnesses by inserting the individual pins at each end of a lead. Connect up an ohmmeter. Resistance should be low (less than probably 0.1 Ohms), and when you shake, wiggle, push, etc on the cable and connector body, the reading should remain stable.
3. Relax, have a beer, and repeat for every *&!ng wire in the EPS related harnesses.
4. Check for a possible high resistance ground wherever the rack and module are grounded. I would loosen the bolt or nut on any ground lead, clean the connection, an possibly even use the compound electricians use when connecting aluminum wire to copper outlets (I think it was called No-Ox, but I haven't done that in years.)
A final word. About 5 years ago, my '96 would suddenly pull to one side for a few seconds while driving at highway speeds. It seemed to happen after hitting small bumps, such as the strips between sections of pavement. I pulled the connectors off the EPS rack and they all looked clean. Problem occurred once or twice more, then went away & has been perfect ever since (5 years and 12 - 15 kmi). I just hate unexplained events like that.
So I feel your pain somewhat, but yours is worse since you haven't gotten it to go away yet.:frown:
