Need fast advice on throttle surge on 2016 C

It sounds like it is motoring the engine- meaning, the electric motor is deliberately spinning the gas engine (with no fuel or spark) to bleed off electricity, which can happen when the ECU thinks the battery charge is too high for the current battery temperature. This doesn’t actually indicate a failure per se, just that you’re operating near a temperature limit. You may find that symptoms subside with more air conditioning, since the battery breathes the same cabin air you do.

Have you cleaned the battery cooling fan? Pop the cover off, clean the grating, then check the foam filter thingy to make sure it isn’t blocked, and lastly pop it off to make sure there isn’t a wad of fuzz stuck in the actual blower itself. Keep it super clean for best battery life.

 

any dash lights?

the throttle body shouldn't need service at 52k, but i'll withhold judgement since something is obviously wrong.

you definitely don't need a bottle of elixir.

maybe an egr inspection is in order

 

I can’t remember where I first read about it, sorry. I wouldn’t be surprised if it was in the back of the owners’ manual somewhere, but mine isn’t around to confirm right now. The feature probably has a more official name too, but I don’t know what it is. From your added details it really sounds like that’s all this was.

The computer will take that step (and some other odd behaviors) to preserve the long term health of the battery. The downside is the annoying noise coming unexpectedly when you’re off-throttle.

More air conditioning solves the problem two ways- it uses a lot of electricity, so the battery is less likely to top up at stops, and of course it cools the cabin so the battery temperature doesn’t go too high.

Enjoy the ride!

 

You're mostly right. The computer can record some conditions without triggering the lamp, but generally these are emissions compliance situations, not 'YOUR CAR IS BROKEN' situations.

I still don’t think anything was ever actually wrong. The battery was simultaneously too warm and too full for long-term health. The computer solved the problem by partially draining the battery in the most harmless way possible- motoring the engine.

You can be certain that it had previously tried jacking up the speed of the battery cooling fan, but if the cabin interior was broiling hot then this method would not have been effective, so it tried plan b.

 

The engine flare on stepping off the accelerator is completely normal. We've tried to get to the bottom of it, hours and hours of data logs mapping what the systems are doing, and have never been able to find an answer. They'll do it for a few minutes, and then revert to normal. Best assumption is it has something to do with "battery maintenance," as the battery doesn't charge, nor discharge as quick as it should during these "episodes." Battery SOC, nor temperature plays no part, but in hot environments, it seems to do it more, regardless of battery temperature...

If you've ever seen the OE service information, there's a lot of [TMG PROPRIETARY INFORMATION] redaction in there, where they dont' want to specify thresholds for this or that. This is one of those situations.