BMW Repair: Shifting issue, 1997 bmw 528i, oil leaks

Question
Hi Don,
My 16 year old daughter has a 1997 BMW 528i which she loves, but now she is crying( as they do sometimes) because the car she worked and saved toward is acting up, and we are NOT mechanical and have no idea why. The car will be running perfect( and I mean perfect, runs excellent) but at random, the RPMS will go way up by itself, and the gear shifter will change randomly from D to SL, and back and forth several times. She pulls over and turns the car off, and usually when she starts it back it will be fine, like nothing ever happened. Then oddly enough, it will happen again, about 1-2 weeks later. We are VERY concerned over the transmission. Lord knows we don't have the money to replace it. The car has 112K miles and is an automatic. The oil changes, etc are up to date. I have read on line about the Crank or Cam position sensor. Do you think this could be the problem? If so do you know what it costs to replace either of these? Oh yes, once for a very brief period the "check engine" light came on but just as quick it went back off. Even when the car is acting up like this, if she puts it in 3rd gear it runs great. Then a few mins later she will be able to put it back in D and all is well, until the next episode.
Can you please offer any advise? Thanks in advance for your help.
Jessica's mom
Linda

Answer
The first step would be to be why the check engine light came on.The code,although the light went off,will still be in the computers memory.You mention the transmission shifter randomly goes from D to SL.Does the transmission itself shift or is it just the indicator lights just move?
So your first step is to find out why the check engine light came on,it could just be a bad connection.About the idle concerns,make sure the throttle plates are clean of oil,dirt,etc.If you have any oil leaks those too need to be tended to,as they cause an unmeasured air leak.