I brought my 2001 BMW 325i to a non-dealer auto mechanic because my car was stalling on occasion.  He ran diagnostics and came up with a fault code of P0340 "camshaft position sensor".  He quoted about $350 to fix it (not including the diagnostics - diagnostics cost me $114).  I said I would think about it.  I immediately filled my tank with high test gas (typically only fill it with 89 octane), thinking that perhaps this could contribute to poor performance.  I have driven the car for 3 weeks without it stalling - until yesterday, when it stalled 5 times on the commute home.  This morning, it ran fine!!!  My question is why are the symptoms so intermittent?  And, is there something I can do, besides replacing the sensor, that will allow the sensor to work properly?  Also, I was told by someone else that there is more than one camshaft sensor -- is this true?

Thanks!!!