I already own this car for 3 years, but I never found a difference when pressing the Power or 'sport' button.
I read some posts and I understand there must be a different throttle response and gear change behaviour.
I have a 1998 GS300.

Can somebody point where to look? Fuses are ok, but I have had a strange problem with some relays (I had to clean them in order to work again). This latter problem seems fixed for months, but it has been culprit for many problems!

 

Does the light indicator on your dash come on when you press the power button? There should be a green light saying ECT PWR or something like that on your dash when you press the button.

Does the light come on but theres no difference in throttle response or is there just no light at all when you press it?

 

The most noticeable thing the button does is have the transmission hold gears a little longer, it's intended more for helping a heavily loaded car than it is for "sport."

 

I am curious, it does feel faster with it in sport mode, does anyone know if it affects the 0-60 time on a stock GS?

 

Absolutely not. If you have the pedal floored, it shifts at the last possible moment whether or not the transmission is in "PWR" mode.

All it does is alter the shift points a bit. It'll kick down a gear easier when you ease on to the throttle and hold shifts longer as you accelerate partial throttle.

 

I really don't feel a difference. How can I test this, so I know it is functioning? Maybe look at revs when gearing up while accelerating?
The green ECT Power lits up when I press the button.

 

I've driven a few GS300's its a lil snappier shifting in PWR mode thats it. In the GS400 or GS430, its more noticeable throttle response cuz the car is more powerful.. (In the 400/430, with it in Normal mode shifting is very smooth vs PWR mode, the car is wringing everything its got to produce the most power and quicker shifts..

 

Get on the highway when there's not a ton of traffic.
Cruise along at 65 or 70mph (whatever is legal) in "D"
With the transmission in "NORMAL" mode, slowly press down on the throttle to accelerate. Note how aggressively you have to press the throttle to get it to kick down into 4th.
Slow back down to 65 or 70. Now switch the transmission to "POWER" mode and do the same thing. You should feel it kick down into 4th much sooner and with less pedal input.

I'm pretty sure that the ECT PWR mode has absolutely nothing to do with throttle response or horsepower. It's just a different map for the transmission ECU. It has nothing to do with how the engine runs.