Mercedes Benz repair: 1985 mercedes 380sl, vacuum problem, vacuum leak

Question
I have replaced the break booster and booster vacuum hose within 6 months.
When I stop at the red light, the idle will goes up from 650 rpm to 1100 rpm and down by itself more than once sometimes depends on the length of the red light time.
What could be wrong? Thanks.

Answer
This is most likely a vacuum problem. The best thing to do is make sure ALL vacuum lines are connected securely. The next step is checking for a vacuum leak somewhere.....the easiest way to do this is to start the engine. Then take some carb&choke cleaner and spray a little around each vacuum line and vacuum fitting in the engine bay while the motor is running. If the idle increases when you do this, then that area is where vacuum is leaking and you can focus your attention there to correct the problem.