Posted February 27, 200718 yr comment_200825 Hi all: I haven't started digging into this much yet, but searched and didn't find my exact symptoms. Here they are:1) While driving along and with everything working fine, my tach will all of a sudden jump to much higher numbers and then move erratically.2) At the same time that the tach act up, I'll notice some rough running - even at speed I can hear the car missing. Althought the engine starts running rough, it's obvious the tach readings are incorrect (jumping very quickly and reading 5000+ RPM when I'm in 4th gear at 50 MPH, for example).3) If I come to a stop while this is happening, the idle is very rough and generally slow.4) Here's the fun one: this can happen for a few minutes and then just stop and all will work great. Also, the last time it happened, I turned off the ignition, restarted and all was well (rebooted...).Details: Stock 1975 280Z with 186K miles which has bene sitting for a few years up until the last two months.My initial thoughts: Definitely electrical and something that can impact both the tach and the ignition. I think this must be a connection-type problem at the ignition control unit (ECU in modern terms, I suppose) or something else electrically 'global' like the voltage regulator or alternator.My plan: Check all obvious connections to these three major components, then go from there if I don't find something loose.Any thoughts or experience related to this? Does the tach get its reading via the control module? My car doesn't live at home, so I haven't had a chance to chase this down since it happend on Sunday; but I wanted to bounce this off the group... Link to comment https://www.classiczcars.com/forums/topic/23447-erratic-tach-missing-and-idling-poorly/ Share on other sites More sharing options...
February 27, 200718 yr comment_200828 check for any side to side movement of the rotor shaft inside the distributer. Link to comment https://www.classiczcars.com/forums/topic/23447-erratic-tach-missing-and-idling-poorly/#findComment-200828 Share on other sites More sharing options...
April 20, 201311 yr Author comment_421075 Update...six years later. I never did get this solved with the stock engine, but it recurred with the stroker installed. It was traced to the ignition box in the passenger side footwell. A good condition replacement unit completely solved this problem.Yes, it's an old, short thread, but I wanted to close the loop in case anyone else had similar problems. Link to comment https://www.classiczcars.com/forums/topic/23447-erratic-tach-missing-and-idling-poorly/#findComment-421075 Share on other sites More sharing options...
April 20, 201311 yr comment_421081 You can also use an HEI to replace the stock box. Link to comment https://www.classiczcars.com/forums/topic/23447-erratic-tach-missing-and-idling-poorly/#findComment-421081 Share on other sites More sharing options...
April 20, 201311 yr comment_421086 Now that's someone dedicated to following up on a post! Link to comment https://www.classiczcars.com/forums/topic/23447-erratic-tach-missing-and-idling-poorly/#findComment-421086 Share on other sites More sharing options...
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