central locking system/450sl
 

My locking system works partially. It will lock both doors but will not lock the gas flap. How can I test it. If this is a vacuum leak will it affect the engine idle. Thanks.

Most likely the gas door element has gone south. Much less likely is that the line leading to it has a leak or a coupling has slipped off. I would start by disconnecting the line and using a vacuum pump to see if the element holds a vacuum.

If the door locks still work, it is probably not affecting the engine.