Rough idle - discovery 1

Hello guys, good day …!

I am having an issue with idle. The RPM goes up and down. In cold start By Default the RPM idle on 900 to 1100 RPM. When stopped in traffic or signal light the RPM goes up and down and the engine stalls. when the car comes to a complete stop on Gear D this happens. In neutral the idle is up and down for 1800 and down to 600RPM but it doesn’t stall the engine.

Only last change done was replaced the vacuum advance unit on the distributor.

Appreciate your support on this as usual.

Check your throttle position sensor. If it doesn't correctly tell the ECU when your throttle valve is closed it won't activate the idle control valve.