There are many reasons why your vehicle may be losing power, especially when accelerating. Some of these common causes are: Mechanical problems such as: Low compression, clogged fuel filter, dirty air filter, clogged Exhaust Manifold.Malfunction of actuators such as: Bad injectors, bad fuel pump, bad spark plugs.
The transmission is designed to effectively multiply the engine torque so that it can move the car.So to answer your question, the car does not “lose power” when you put it into gear, it just doesn't have enough torque to move it until you give it more torque by opening the throttle.
What Does the “Engine Power Reduced” Warning Light Mean? The Engine Power Reduced warning indicates that your car's performance has been limited to avoid damaging the engine. Your car's computer, often known as an electronic control unit (ECU), triggers Reduced Power Mode when it detects a system failure.
The most likely issue is a clogged fuel filter. While the fuel filter is the most common problem with the fuel system and is the easiest to fix, a lack of power could also point to issues with the fuel line or the fuel pump.
Among the causes of poor acceleration are clogged fuel injectors and/or inadequate fuel pressure/volume. This can cause the vehicle to accelerate slowly, or even sputter and stall, especially at high speeds. A clogged fuel filter can also restrict the amount of fuel that reaches the injectors .