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Had a funny idle this morning. I have a 2.2k ohm resistor in my iat sensor but I dont see how it would have anything to do with it. Cranked up and drove to work this morning and all was fine. Got in my truck a couple hours later to go to my next store and truck cranked up and idled fine a few seconds then it idled to about 950 or so then back down to 800. It did this on and off for a minute until I put it in drive. Then got to my next store and it was doing the same thing when I parked, it would idle like this for 3-5 seconds high then 3-5 seconds low. I reset the apps and then came back out in a few hours and the truck was doing the same thing. Next store I reset the apps and it has been fine since. Not throwing any codes either, any idea's?

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Well with the warmer (70+) I havent had any trouble but it got cold (50) over the last couple days and its been acting up again. I pulled the 2.2k resistor and hooked the iat sensor back up and it didnt change anything. I noticed when its cold out, my alternator stays down around 12v when im idleing but then gets up to 14 when I start driving. When the truck idles itself up the volts rise and then they fall when it idles back down. I resset the apps several times yesterday with no luck but after it warmed up in the afternoon it ran fine. Maybe a bad alternator?

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Try having the alternator bench tested and make sure to have them check the diodes for function. Just because voltage is present doesn't mean it not leaking AC current through 1 diode which could be enough to drive the ECM, PCM and VP44 nuts...

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I will, also got a 1688 today but I erased it and it hasnt come back. I bet its the alternator.:thumb1: My temp gauge is also fluctuating sometimes, it will never get up to temp and fluctuate from 160-180 or so, seems like this idle is crappy when this is going on too. I have heard that cummins has a new thermostat to fix this issue so I ordered one. I think he said it was a 83 (181.4 f)degrees celcius t stat but as far as I know, mines a 190.

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