Hi and thanks for using 2CarPros.
The issue may have been caused by the plug replacement. If an engine vacuum hose was damaged, disconnected, or missed, it can cause a similar problem. Additionally, there is a component called the idle air control valve (IAC). The IAC is responsible for maintaining engine idle speed. Basically, with fuel injected cars, the throttle plate fully closes when you are off the gas. However, the engine still needs air to run. The IAC allows a metered amount of air to enter the engine. When they start going bad, the engine idle can go up and down.
I apologize, but this vehicle isn't offered in the US so I don't have technical information on it. However, what I described is relatively standard on all vehicles produced today.
What I suggest is this. First, confirm that no vacuum likes were damaged and +make sure the air intake tube that runs from the air filter box to the throttle body is properly attached and not allowing unmetered air to enter the engine.
Here is a link that shows how to check for engine vacuum leaks:
Since the IAC is operated electrically, check and confirm the plug is properly attached. Here is a link that shows how to replace one. It is general. However, it will help you identify the one on your vehicle. By the way, the IAC is mounted on the throttle body.
Here is a link that discusses high idle issues:
I hope something here helps. Let me know if you have other questions.
Saturday, January 26th, 2019 AT 8:25 PM