Is it normal
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Intermediate
Joined: May 2025
Posts: 25
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From: Ocala Florida
Is it normal
Is it normal when coasting for the rpm’s to flutter up and down from 1200ish rpm to 800 over and over. I have a video but it keeps telling me it’s an invalid file. https://share.icloud.com/photos/086Q...696ghAersuvYNg
Instructor
Joined: Aug 2009
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Not sure what year Vette you have, but if you have an automatic trans, cruise control set, and the RPM is varying that much it sounds like either you need the triple flush done (get rid of the original hygroscopic trany fluid for new GM fluid), or you have an overall torque converter problem.
A corvette dealer can run a PICO test on the tranny to determine the prognosis.
A corvette dealer can run a PICO test on the tranny to determine the prognosis.
Stick Shift Enthusiast
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From: Troy & Dearborn, Michigan
I've seen a "rough idle" with that type of flutter from time to time. There was a thread on here a while back, pretty sure its normal. Not sure if it should do that while driving though.
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From: Cape Coral, Florida
Not sure what year Vette you have, but if you have an automatic trans, cruise control set, and the RPM is varying that much it sounds like either you need the triple flush done (get rid of the original hygroscopic trany fluid for new GM fluid), or you have an overall torque converter problem.
A corvette dealer can run a PICO test on the tranny to determine the prognosis.
A corvette dealer can run a PICO test on the tranny to determine the prognosis.
A PICO test ??…do you mean diagnosing this using a PicoScope DSO ??…dealers only use a scope for NVH…you can diagnose this if it is an Auto looking at Torque Converter data PIDS…seeing if it is engaging or disengaging by itself…usually the crankshaft position sensor is the input for the Tach.
Last edited by C5 Diag; Aug 2, 2025 at 12:40 PM.
Thread Starter
Intermediate
Joined: May 2025
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From: Ocala Florida
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something similar, as i take foot off gas, as car slows down i feel it downshifting to 2nd/15mph!!
more pronounced/higher rpm if i ds with paddles!!
more pronounced/higher rpm if i ds with paddles!!
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Lol, assuming people have a YouTube account. I have a Gmail and even I don't have a YouTube account (on purpose). I'm sure there are people who have no idea how to use one even if they did have it.
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From: nashville TN
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Just to be clear, I read your post to say when “coasting”, not just idling, or downshifting when coasting to a stop. If it was my car I would take it to a level highway, get up to speed (so it is in 8th gear), engage the cruise control and watch the tach. If your RPMs are varying from 800 to 1200 RPMs at that point it is NOT normal. That means the torque converter is acting abnormally and needs either the triple flush (has this ever been done), or a thorough examination with the right equipment is necessary to determine exactly what is going on.
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From: Troy & Dearborn, Michigan
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I strongly suspect the OP is in the early stages if the transmission “shutter” issue. Although there isn’t any mention of shutter or vibration it is often very subtle in the early stages. I have seen the PICOscope used to sort out if the NVH symptoms were originating from the engine or transmission, in conjunction with other diagnostic procedures. I still strongly suspicion that a 400RPM variance (RPMs going up and down) when not downshifting or coming to a stop is a torque converter issue, and I strongly suspect that it is the commonly mentioned shutter issue that requires the triple flush procedure to eliminate both the shutter and the variance in the observable RPMs..
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Don't ever recall having my RPMs flutter like that.