Here's a brief update on this part of the thread:icb wrote: Fri Mar 22, 2024 10:33 pm Is anyone else having or has had the issue where you set the speed and the car instantly picks up 5-10 MPH? This behavior only started after I replaced the last two original 2.2 µF/60V electrolytic caps (one of them had been leaking). I had replaced the other electrolytics previously and the speed control was perfect after that repair. Then it stopped working again, that's when I did these two, and that's when the speed increase started happening.
My speed increase was due to the cable having a wee bit too much slack in it. I should have checked this first, but I had removed and re-adjusted the cable many other times before, and hadn't noticed any difference in the speed control behavior, so I had thought the system wasn't sensitive to the cable adjustment.
Just prior to replacing the last two original 2.2 µF/60V electrolytic caps (a brief period where the speed control was not working), I had been chasing an idle problem, and to ensure the speed control cable wasn't affecting the idle speed/throttle, I had loosened off the adjuster a fair bit, leaving 5-8mm of slack . Last night, I saw something in an old 911 post somewhere about removing all the cable slack, and just to see what would happen, I re-adjusted the cable to leave about 2 mm of free play. Now the speed control engagement is totally seamless and perfect.
I hope this info might save someone from the PITA of unnecessarily removing the controller under similar circumstances in the future.
I still plan to draw up the controller schematic (actually there are at least two, maybe more versions) and post it here at some point, because we really do need it.