Been searching google for a few weeks trying to identify the cause of this.
2005 Enthusiast 6mt 85k

Going over 25, under 90.

Hit "On/Off" - Cruise light comes on

Flip the switch to "Coast/Set" - Set light comes on. Solid.

YET - The car does not hold speed. Lift off pedal, car coasts.

Tap the clutch pedal - Set light goes off.

I remember this working a while ago, not sure when it stopped.

Did have a problem with the map lights and the BCM, which was fixed by opening both doors and unplugging the battery for a bit. From what I can see in the FSM, the cruise control is primarily controlled by the ECU.

I do have an Osiris tune, which we have made a couple updates one and off, but the tuner states there should be no way for him to disable the cruise and have the lights still come on.

Since I last saw it working (car was parked most of the winter), I did brembos, bucket seat, and spark plugs. Was careful to unplug battery before anything. No lights on dash.

Anyone have any possible explanation? Debating starting throttle body reset and or new throttle body, or going back to a stock tune to try it out.

 

The cruise control switch on your steering wheel is going to pulse out to the BCM, which then instructs the ECU (PCM) to engage the cruise control. Any issue along the entire control chain could be the culprit here, including the new Brembos, which could be sending an out-of-spec signal to the ABS control module, which is confusing the VDC, which would then interfere with the cruise control (though I'm guessing an ABS fault would throw an idiot light.)

So many problems pop up with Osirus tunes with so few gains on these cars. I honestly don't know why people bother.