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Q: will not stay idling on 1990 Mercedes-Benz 560SEL

The car runs good and strong but will not stay running unless the gas peddle is gently held its like it needs to be idle up i can hold the air intake flap down 1/4 inch and it will idle just find im just lost on it
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These vehicles have a mechanical fuel injection system that is very susceptible to vacuum leaks. There are also some adjustments that need to be performed in a sequential order for everything to operate correctly, so if you're not familiar with how the system works, you may be better taking this to a MB shop. However, here are some tips.
Check for vacuum leaks, especially at the injector seals. Fix any you find and make sure the fuel mixture is set correctly. This engine has an idle valve that controls the idle speed, it may be that the valve is sticking or bad. Also, check that the throttle body is cleaned and adjusted properly.
Check the fuel pressure relay, it must be seated very snug in the socket. Most times this the problem
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