Hello,
The spark plugs coming out could be a stripped thread in the cylinder head, or they are loose. However, when they are able to wiggle free, they create a large vacuum leak, and that will raise the idle significantly, or cause the engine to stall.
If you are seeing the ABS light, in conjunction with an idle up to around 1800RPM, you likely have an issue with your OVP relay, which protects your idle circuits from over-voltage.
This may mean the relay is bad, the alternator is over-charging, or there is an open connection in the circuit.
You will likely want a technician to test and diagnose the circuits, so you do not replace the relay for no reason.
Also, you NEED to have the spark plugs addressed. If they are falling out, there is a chance the engine is sucking in metal shavings from the spark plug or cylinder head threads.
If you have any other questions, or need more information, let me know, or, if you prefer one of our certified shops diagnose the issue, see the link below:
http://repairpal.com/mercedes-benz-within-10-miles-of-reddick-florida-32686
