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Discussion Starter #1
Why why why does my tachometer needle rise and fall ever so slightly at idle?? and now that it has gotten colder out, ive noticed that it wont happen ALL the time when its cold, but it still is happening. Anybody know what the hell is causing this??
 

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I believe the grid heater cycleing effects the electical system to the point where it effects the tach and everything else. I doubt the fluctuation occurs after the truck warms up.
 

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I have the same problem as well, mine does it when its warm too. I think it is my ac clutch kicking on and off
 

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i am almost certain that it still occurs after the truck warms up. but im going to observe it today and get back to ya, motorboat. maybe i should mention that i am highly suspicious of having a possible out of spec valve(s) or a bad injector currently as well. Doubt it, but Could either one of those issues cause a small fluctuation like im having? thanx guys
 

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i am almost certain that it still occurs after the truck warms up. but im going to observe it today and get back to ya, motorboat. maybe i should mention that i am highly suspicious of having a possible out of spec valve(s) or a bad injector currently as well. Doubt it, but Could either one of those issues cause a small fluctuation like im having? thanx guys
Let us know what you find. I have the same deal going on.
 

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do the volt's go down at the same time? mine do because of the grids.
 

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Discussion Starter #8
its been intermittent from what i'm noticing so far, im not sure if voltage is fluctuating at the same but, i doubt that its due to grid heaters. however, i had two bad batteries a couple weeks ago and the "check gauges" light would come on upon startup and go off and on for a few minutes after startup. after two new batteries, the light will still come on upon startup and stay on for about a minute. i can make it go off faster if i give some throttle and hold it. im wondering why this is still happening; alternator or voltage reg most likely? im not convinced that the two are related. ill let you guys know whats going on.
 

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Yea me too, my volts drop too. I thought the heater grid was to get things started and the turns off after it's on? and even if it's a huge current load why does it drop the rpms there's no ignition system to affect the engine , could it be the alternator? I hear pops and clicks too( like relays or clutch...) . Seems not to do it when the truck is warm. I'll unplug the grid heater and see what happens
 

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my truck does the same thing but only when i have the defrost turned on. if i turn the defrost off it stops doing it. does the truck have any type of lope at high idle? mine lopes if i use the cruise to go to high idle but it only lopes and the tack only jumps a lil when my defrost is turned on. turn defrost off and lope and tack both stop. its your grid heater kicking on and off. something to try at least.
 

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It's probably the a/c kicking in. It comes on to dry the air when in defrost mode as well.
 

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If you shut the interior fan off and the rpm does not wander (when warm) then that's it.
 

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Discussion Starter #15
i can tell you this, somethings up with my a/c because it doesnt kick on when activated so if it wont do that i doubt that its the a/c. but i can see it being caused by the interior vent fan. i have the heat on constantly so its possible, ill turn that off and see what happens after it warms up. also, the engine does not lope. its just showing slight fluctuation of rpms on the tach. sounds like a bunch of us are seeing the same thing. there's been times when i look down and the tach is steady at idle. so just have to pinpoint when that is! **(just to clarify, we all are talking about slight tach movement "at idle" correct. for me, rpms remain steady through the rest of the range) Unless im not noticing it?!
 
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