My 2001 325xi began to idle roughly....took her in and they replaced the plugs, fuel filter and tuned her up.  Drove great for a couple days and then the 'check engine light ' came on and she was back idling roughly.  They replaced  the crankshaft sensor and she drove great for a day but now she idles so bad at lights she stalls and of course the sensor is back on.  Any suggestions?