Weird 100rpm jump at idle when stopped in drive

[lxs123]

Has anyone else noticed a weird intermittent rpm bump of about 100-150rpm when stopped in drive? It happens every 45s or so. I have no accessories on.

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[Kielly]

I think it may be the same thing I noticed the other day, if so I'm glad I'm not alone and I hope it's oddly normal. I couldn't tell if it was a spike or a drop but the gauge don't really move or hardly moves, but you can feel it and hear it with the music off. It'll also vibrate the shifter in my 6M. Tried to video it but you can't really see it on the video.

 

[ridetime]

A/C compressor cycling? Or electric fan cycling??

 

[lxs123]

I think it may be the same thing I noticed the other day, if so I'm glad I'm not alone and I hope it's oddly normal. I couldn't tell if it was a spike or a drop but the gauge don't really move or hardly moves, but you can feel it and hear it with the music off. It'll also vibrate the shifter in my 6M. Tried to video it but you can't really see it on the video.

If its doing it in 6MT then its not transmission related, assuming that you are in neutral when at the stop light. I wonder if this is part of ecu learning and adjusting the maps to suit our driving style.

 

[lxs123]

A/C compressor cycling? Or electric fan cycling?? Wierd.

None of the accessories were on. The electric fan kicks in 5-10s after the surge, therefore i doubt its the fan.

 

[Kielly]

If its doing it in 6MT then its not transmission related, assuming that you are in neutral when at the stop light. I wonder if this is part of ecu learning and adjusting the maps to suit our driving style.

Only time I've noticed it was when I was idle minded while idling the truck in neutral with parking brake on. I'll have to pay more attention to see if it's an all the time thing or an occasional thing.

I got worried that day that the engine was acting up. Maybe so something to do with the ecu but I've got 7000kms on her now, if she hasn't learned my style by now just as well she never does lol.

 

[jmalski4865]

A/C compressor cycling? Or electric fan cycling?? Wierd.

My electric fan cycles even when I turn off the ac. Just running the vents. Annoying

 

[jmalski4865]

I shut down all the climate controls and radiator fan stops running. Still getting a small amount of air through the vents

 

[lxs123]

Has anyone experience a jolt in transmission when decelerating to a stop? This only happened once but i worry it may be related to my initial post about rpm spikes at a stop.

 

[ldudiaz]

Has anyone experience a jolt in transmission when decelerating to a stop? This only happened once but i worry it may be related to my initial post about rpm spikes at a stop.

The jolt has happened to me like 3 times when slowing down for a stop

 

[RFish]

I feel like it's just an aggressive down shift when slowing down. I've watched the rpm gauge and noticed this too.

 

[theKurt]

I won't claim this is it, but maybe. We have both port and direct injection which alternatively engage at various states of engine speed or load, and direct injection is known for causing carbon buildup. The engine has a "self-clean" mode when at idle to remove these carbon deposits. This might explain the RPM changes. In which case, hooray.

Also, check your system settings. Mine was set to use A/C when I pushed "auto" for the climate controls. Therefore, you don't necessarily need to see the green light on the A/C button for it to turn on. It could be cycling on and off without you knowing.

As or the electric fan, previous gens had a mechanical cooling fan attached to the crank and the pulley system. These are wonderful at sapping engine power with their inertia and wind resistance. I for one am very happy to have an electric fan now even if it cycles on and off to keep the coolant at the right temp.

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