Car was running like a dog last night, and I noticed the Traction Control light was lit up on the instrument cluster, this is new. Pressing the TCS button doesnt change the light.

When turning the ignition on, the light illuminates for 2 seconds, and goes out - this indicates that the system is functioning normal per its self check, but within 2-3 seconds of the engine starting it lights up again -before the car even moves. If it lit up when the car was moving I'd be OK with that, as it probably detected a mismatch between ground speed on different inputs, but the issue comes up without the car moving. hmm!

Interestingly this morning, when I started the engine there was no TCS light and the car was running like a dream - for about 30 minutes, then the light came on and it started running rough again.

It sounds like its down a few cyl, possibly base timing and over-fueled.

Any ideas?

ABS working alright?

I'd be checking/cleaning the ABS tone rings and sensors. That's where the TCS get's it's differing speed signals from, it could be one sensor is getting a bad reading indicating movement, even when there's none.

And the engine will run rough, as the TCS is telling it to retard. (on B-series it can tell the throttle to close up)

ABS is working fine. I'm partly with your thought though, I was thinking the same thing - though the fact that it self checks OK, but then throws a light immediately after starting the engine is somewhat confusing.

It's going in on Monday, lets see what happens.