I started up my 740 Gl today and I noticed that when it was in park, the idle was would rise to about 2500rpm and then after a couple of seconds it would drop to about 1500rpm. When I put the car in drive it would shake pretty hard but the idle seemed to stay at about 1000rpm. Im pretty much clueless. Any suggestions?

 

Have you checked the throttle body for cleanliness and the throttle position sensor switch for correct function? let's see, how about the Idle air control valve? It might need cleaning. Air filter too. In fact all fitlers. And the positive crankcase ventilation system perhaps. Exhaust Gas Recirculation valve perhaps dirty. Vacuum lines, have they been checked for integrety faults?