Engine de-throttles when transmission shifts when cold

[BigLexusMN]

I have a new to me '17 LC with the 8sp transmission and 80,000 miles. I previously had a '13 LX with the 6sp.

When it is cold outside (30-50ish F) and the engine and transmission are cold, as I accelerate down the street, each time the trans upshifts, the engine de-throttles momentarily during the shift. As it warms up, the de-throttles are less abrupt and when warm, doesn't exhibit this at all and performs as expected.

I don't think anything is wrong because it becomes less aggressive as it warms and goes away altogether but it is annoying as it throws you into the seatbelt each shift and there are a lot of them in an 8sp when accelerating. I can't catch it on the tachometer because this occurs when the trans is shifting so the RPMs drop a bit normally during this process.

Does anyone else have this experience or is the vehicle programmed to do this? I've owned a lot of vehicles and never had one exhibit this.

 

[Sandroad]

That’s definitely not how my ‘17 8 speed shifts and the engine does not “de-throttle”. It should not throw you onto the seat belt all 7 shifts when warming up. If the engine were to “de-throttle” enough to throw you into the seat belt you would surely see it on the tach. And 30-50 degrees F is not very cold. First, make sure the transmission TSB has been applied to your LC. That’s for rough shifting in the lower gears (typically 1-2 and 2-1), but it’s bad enough without the software update that it could be affecting your feeling about all shifting. There are lots of posts on here about that TSB and the need for it on the 8 speed. Then do a fluid drain/fill and make sure the fluid level is correct. See if those improve shifting. It seems likely to me the problem is with the transmission and not the engine.