Hi Guys, I searched this forum but I couldn't find the answer so I started a new thread. Thank you in advance for any feedback.

I acquired a used S350D few months ago. Had some hard time to replace the glow plugs since one was stuck in hold and wouldn't coming out. Eventually I left that one there, and I was able to start the car with five new plugs. But I noticed a new problem it didn't have before. When engine is cold, the idle speed is normal. But when the engine temperature got to a normal level, the idle level will goes up to 2000 RPM which make the car is not safe to drive any more. The idle was OK before replacing the glow plugs. Is it possible I broke any vacuum line? But it doesn't explain when idle was normal when it just started? I am completely lost. Can any of you give me some directors? Thank you!