Re: Intermittently rough
Almost all electronic components use the data bus: PCM, BCM, AC head unit, EVIC, instrument cluster, radio/CD changer, driver door module, passenger door module.
Not always a code will be set when a crank or cam sensor starts failing. But if it intermittently shorts internally, it can make the PCM to short out the data bus. It is really the speedo which is acting up, not the tacho?
It can also be a problem inside the PCM.