1998 Chevy Malibu Check engine code

I have a 1998 malibu with a 3.1L engine. It started running rough at low speed a couple of weeks ago. Sometimes at highway speeds I notice a change in rpms. At the same time the service engine soon light appeared. Autozone read code P1374, which was read to be the Crankshaft positioning sensor. My mechanic told me it can't be that because the engine would stall or even not run. He put his more complicated snap on scanner on it and told me it had a bad charcoal canister. I don't want to dump a whole lotta cash in this vehicle so I am hesitant to pay him to replace this cannister only to find out that wasn't it. My question is: will a bad cannister have an effect on the engine performance/and throw a crankshaft positioning sensor code? Any help appreciated.