I'd just check your Idle Control Valve

Follow these steps to check it.

First of all, nine volts or more should be present between the black/yellow (+) terminal and green/black (-) terminal of the valve leads while solenoid valve is being activated.

1. Disconnect idle control solenoid valve electrical connector.
2. Disconnect upper hose to solenoid valve from manifold and apply vacuum to hose. Valve should hold vacuum.
3. Continue applying vacuum to hose and briefly energize valve by connecting battery positive terminal to the black/yellow wire terminal and negative battery terminal to the green/black wire terminal. Valve should not hold vacuum when energized.
4. If idle control solenoid valve fails to perform as outlined, valve is defective.

I had a similar problem with my M3 and a jumpy idle, I just cleaned the idle control valve and seafoamed the car and problem was fixed.