C250 td Engine running issues.

I have just picked up a c250 td sport estate. To replace my saloon.
was all good upon pickup and test drive but upon getting home and switching off the engine over ran when the ignition was switched off. this seems to be the case 9 times out of 10.
Then the following day when starting the car the EPC light stayed on on the cluster. initially the car was what i can only describe as "in limp mode". Upon switching off and restarting the light stayed on again but without power loss then cleared after about 10 mins and was not seen again. until the car was restarted the next day.
The EPC light and engine over run persist.
The car has been adjusted for use on SVO i.e. timing advanced. so I'm told by the previous owner. Although i will only be running diesel.
I have also noticed that the EGR has been disabled by plugging of the actuator line and looking at the fuel lines off the fuel pump it appears that some of the lines have been rerouted i.e. one missing off the L/H side of the fuel filter housing.
Any advise or info on putting it right would be greatly appreciated.