If your vehicle is showing lack of power or sluggish acceleration, here are the most likely causes and the parts you'll need to fix each one.
A severely dirty air filter restricts the amount of air entering the engine. Without enough air, the engine cannot burn fuel efficiently, resulting in a noticeable loss of power.
Spark plugs ignite the air/fuel mixture. If they are worn out, incorrectly gapped, or if the ignition coils are weak, the engine will misfire or have incomplete combustion, causing sluggish acceleration.
The MAF sensor measures incoming air to calculate fuel delivery. If it is dirty, failing, or was left unplugged after checking the air filter, the engine computer will restrict power to protect the engine.
Unmetered air entering the engine through a cracked hose or a disconnected PCV line leans out the air/fuel mixture. This often happens if a hose is accidentally knocked loose during other under-hood maintenance.
A clogged fuel filter or a failing fuel pump cannot supply enough fuel pressure under heavy load. The engine will run fine at idle but fall flat when trying to accelerate.
If the catalytic converter melts internally or becomes clogged with soot, exhaust gases cannot escape. This chokes the engine, drastically reducing power, especially at higher speeds.
The engine may be making full power, but a worn manual clutch or a failing automatic transmission fails to transfer that power to the wheels, causing the engine to rev high without the car speeding up.
If the timing belt or chain has stretched, skipped a tooth, or was installed incorrectly during a recent replacement, the engine's valves will open at the wrong time, severely crippling engine power.