fasturner

I recently purchased a 2015 C7 with the Z51 package and magnetic ride control. I noticed a strange phenomenon while driving at a steady 75 mph (cruise control) on a dead flat interstate road. The car would bump up from 1700 to 1850 rpm every 5 seconds, hold the higher rpm for a second and then drop back to 1700 rpm. There was no visible change in speed. When the rpm change occurred it felt as if the car had crossed a small bump in the road simultaneously. The same thing happened repeatedly for the entire trip regardless of speed.
I am not sure if it is an engine control or tachometer problem. It felt like a misfire, but I doubt a misfire would cause an RPM bump up. With the exception of this problem the engine performs fine.
Anybody had a similar issue?

obxchartercaptain

Unfortunately, I believe you have a torque converter problem which happened with a few A8 Transmissions. Hopefully, it is still under warranty. Good Luck

fasturner

It is still under warranty, I will get it to the dealer and have it checked out. Thanks for your help.

joemessman

I believe based on what you described that it is the torque converter issue switching between V4 and V8 mode. May have to be a TC replacement and, or transmission. You should be good on the warranty. Sorry you have to go through this, but take it in right away and get it behind you. Be prepared for 2 or 3 visits. Sometimes the take the least aggressive measures and work up to the more complicated repairs. Good luck and let us know how it goes. AT least if it consistently doing that, they should diagnosis quickly.

ddelallata

TC problem as others above commented.
It happened to my 2017 Vette too and there is a new procedure for some vehicles depending on the year that involves changing the fluid 3 times w/ Mobil1 LV ATF.
I believe that on some 2015 models, the fix still calls for changing the TC .

lakemg

Keep us posted on what they say/do. Hopefully they can fix it with just a 3x fluid flush.

ddelallata

Here's a copy of the bulletin in case your dealer in not aware of the problem.
http://www.corvetteactioncenter.com/...tate-1324.html

bjones7131

Drive the car in M mode using paddle shifter and the RPM and shudder should go away. This is not a fix but will verify your problem is the TC. Lot of owners with this same problem, how many miles? Good luck with fix

fasturner

I tried the car in M mode as you suggested and the problem disappears. When i switch back to Drive it reappears. It goes into Chevy dealer on Tuesday. Thanks for all your help. I will keep everyone posted.