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I have a new to me 2016 and the cruise control “wanders” it will hold speed, but the RPMs don’t stay constant, even on level ground. They will vary 100-200 RPMs, fairly constantly. Is this common, or do I have a problem? My precious C5 and C6 did not do this, but they were both manuals, and this car is automatic.
My 2018 GS does the same, but as I use the hockey almost useless stick tach I don't see the RPM wandering. The speedometer definitely shows it though. Girlfriend absolutely hates following me because the car doesn't keep a consistent speed.
Oddly, following/being followed by my buddy with a Z06, we match speed perfectly. So, at least the wandering is consistent?
I don't think I notice mine really wander unless it's going up or downhill. Usually stays within 1 mile of the speed I set. Maybe the converter is allowing a little slip in between the car giving throttle.
k, reread your original post and your concern isn't speed, it's RPM.
the 8AT is a slushbox, and as such there will be slop in the torque converter. 100rpm isn't terribly concerning at low RPMs, my buddy's Z06 has some amount of slop like this.
the shudder is more than likely the v4/v8 mode switching. go into manual mode if you aren't already and see if it still happens.
the rpm fluctuation is the afm going in and out from 8 to 4 cylinders. drop down into manual and the rpm will stabilize. I purchased the range device 3 yrs ago that keeps it in 8cyl, best money I ever spent.
the rpm fluctuation is the afm going in and out from 8 to 4 cylinders. drop down into manual and the rpm will stabilize. I purchased the range device 3 yrs ago that keeps it in 8cyl, best money I ever spent.
WHile true, youcovered the problem but didn't correct the problem. THe triple flush will fix the issue before it wipes out the torque convertor.
Based on the OPs description I don't see anything wrong with his transmission. He is noticing the engine rpm varying as he drives with the cruise control set, he hasn't mentioned anything about shuddering.
The A8 transmission (actually any slushomatic) will declutch the Torque Converter Clutch when more resistance (such as when going from level ground to an uphill stretch) is encountered or when the engine switches from 8 to 4 cylinder operation or from 4 to 8 operation. When the TCC declutches due to increased load you will see engine rpm vary and if the load is high enough the transmission may downshift. One other thing about the A8 is the TCC doesn't always lock up completely. It is permitted to slip slightly. (See description below)
If you have a manual transmission the rpm won't change the same way since the clutch stays engaged. An increased load will slow the engine until the cruise control can react. If you have a cruise set while driving in 7th gear you will see more of a drop and a longer time to recover, but if you have the transmission in 4th gear there will be a slight drop followed almost instantaneously by a surge to recover lost speed.
Bill
Last edited by Bill Dearborn; Dec 14, 2022 at 11:28 AM.
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Cruise wanders
