Incidentally, I verified my Rostra cruise control speed isn't based on RPM with a very simply test.
In fifth gear I set my speed with the cruise control to 55 mph. I drove for a moment and then tapped my brakes to disable the cruise control. I then put the vehicle into fourth gear and hit the resume button the the cruise control. It cruised at 55 mph.
Thats a good enough test for me and it verifies that it is using a speed signal from the OBDII port and not RPM information.
I'm the kind of person who, when I find a problem too challenging, I walk away from it...at least for a little while. Today, I revistied the problem with getting the ETACS decoder program working on my system. I found I had TOO MANY of the X-Horse drivers installed...apparently Windows doesn't prevent you from installing multiple instances of one driver, but when you do, none of them work. I deleted all of them. I also deleted the manufacturer specific drivers for my MVCI cable.
I downloaded the latest version of the ETACS decoder program and THEIR driver for the MVCI cable and the X-Horse drivers.
I tried to install the X-Horse drivers, but they woudn't install. I DID install the MVCI cable driver with no problems.
I decided to go ahead and try running ETACS decoder and see what happens. It found the cable and I was able to set the COM port and CAN settings, no problem. But, the program was not able to connect to the server to log me in - my firewall was blocking it. I set the firewall to allow ETACS to communicate with the server and I still had 5 writes allowed.
I hauled my computer out to my car, plugged the cable into the OBD port, turned on the ignition, and clicked the 'ON' button on the ETACS display. IT CONNECTED!!!! I then clicked on the 'Engine' tab and all the ETACS items were there; I scrolled down to the Cruise Control setting, changed it to 'Present', clicked on 'Write to ECU' and followed the pop-up instructions. IT WORKED!!!
I disconnected my computer from my car, and took the car for a test drive...I HAVE CRUISE CONTROL!!! (But no horn).
So, I'm happy. A little more tweaking to get the horn working and button everything back up; future plans to enable the fog lights, and disable the engine immobilizer; and maybe I'll just see what kind of trouble I can get into.
Thank you DOAX, and others, for making this possible.
Woohoo, very glad to hear you got it figured out.
They must have changed the wiring on the 2017+ models. The only other wires on my connector are for audio controls. The horn is on a different connector.