Idle speed control valve.
Vacuum leak.
Coolant sensor.
Maf Sensor.
Throttle Position Sensor.
Could be a number of things. Start with the ISCV, give it a clean see if that helps. Your shunt may have dislodged some dirt somewhere along the line to cause some erratic readings perhaps (long shot but just trying to think of a reason as to why it may have started after your shunt).
When you start the car up from cold, what does it idle at? How long before it goes down to normal? If it idles at around 1500, then comes down to 900-1000, that's normal. So take it for a drive and boot it, stop the car then see what it idles at. If after booting it, it idles completely differently, would more than likely be a vacuum leak.
The reason I suggest coolant sensor is because if that's up the swanny, it will think the coolant is never warm enough, and continue to idle high to try and warm it up (as it does from cold). Doubtful it's this, but something to bear in mind.
I'd say it's more likely to be the ISCV, as it does it when the clutch is disengaged. High idles are a bitch.
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