Engine Malfuntion/ Power Reduced
I have a 2003 BMW 745LI.
A few weeks ago, I was driving on the fwy when suddenly, my engine power reduced drastically. I was lucky to be able to pull over to the shoulder and after restarting my car, it somehow reset and drove normally. Ever since, I have had all my oil leaks repaired and in the process, noticed a Bank 2 problem which my mechanic confirmed by switching the motors over. It was replaced with a rebuilt motor and the next day, same engine malfunction. So I went back and we replaced the motor on Bank 2 with a new one. As soon as i drove off, same engine malfunction. It happens more so when I turn right into the driveway or turn right at a light, the power immediately drains. At this point, my mechanic thinks that my wiring harness might be the problem or something is loose.
I have heard a grinding sound when driving under 15 miles/hr including the usual up and down RPM sways. What else can possibly be wrong with this car to cause the Engine Malfunction, RPM wooing up and down at rolling speed and occasional grinding sound at low speed? (Not to mention the blue smoke from the exhaust which I understand but I'm not sure if related to any of this) so I just bought new spark plugs and plug connectors that I intend to have my mechanic replace in case it helps with the misfiring of the engine that causes it it loose power at an idle.