Just have a question about the tach in my truck. This past weekend I noticed that the tach would jump around a little when its at idle. Normally the needle would sit around 700 rpm at idle, with normal variations as the truck idled (probably less than 50 rpm up down movement). Now I am noticing it ill drop down to 500 rpm, then all of a sudden surge back up to 700 rpm or slightly above. I notice when it drops down to 500 it is almost like it shuts off. There is no small movement of the needle at all. It seems like a manual tach if there was something wrong with the drive gears. Anybody had this happen to them. All the gear I'm running is in my signature. I'm running 3 on the smarty. Thanks!

 

Maybe intake headers cycling? or CPS

 

Not familiar with that? What is CPS, and why would the intake headers be cycling?

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If you meant intake heater, that usually doesn't move the rpm more than 50 to 100 or so. Still don't know what CPS is?

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Any other ideas?