It could be any number of things. Fuel control comes to mind as if the fuel system cannot provide the fuel pressure and volume to the motor, you will have issues. Throttle position sensor, mass air flow sensor and a number of other sensors could cause that problem. Just recently, I had a truck that would decelerate when the throttle is pressed beyond a certain point (when you really need it). Normal driving it would work OK, but if you had to accelerate hard, the truck would slow down. It was a bad mass air flow sensor.

Step 1 is to find out if there are any fault codes on the computer. Try a local auto parts place to see if they can scan your computer. In some cases, you need to have a scanner that will read while driving to see what is going on at speed which would require a mechanic to test drive your Land Cruiser. Modern cars have a huge amount of sensors. If a sensor is reporting out of spec for an extended period of time or if the sensor is a significant sensor, you will get an engine light. Sometimes if the fault goes away, the engine light will not come on, but the computer logs the fault.

In some cars, they will coast when off the throttle while others will have engine braking. If it decelerates with the foot off the throttle as if the brakes are applied, then this could be a normal condition for the Land Cruiser. Many people have an issue with this. The automatic transmission can have a lock up torque converter. When it is locked, there is no coasting. If you have ever driven a manual transmission vehicle, you will know what this feels like. The engine itself can act as a light brake with the foot off the throttle.