If your vehicle is showing engine vibrates excessively when revved in park or neutral, here are the most likely causes and the parts you'll need to fix each one.
Engine mounts use rubber or fluid to isolate engine vibrations from the cabin. When they tear or collapse, the engine's torque reaction when revved transfers harsh vibrations directly into the chassis.
A dead or weakly firing cylinder throws off the engine's rotational balance, causing a shudder that scales with RPM. This is often caused by worn ignition components or a disconnected coil after recent maintenance.
The harmonic balancer dampens internal crankshaft vibrations. If its rubber isolator ring deteriorates, the heavy outer pulley can slip or wobble, causing severe engine shaking at higher RPMs.
Mechanical cooling fans spin with engine RPM. If a fan blade breaks off or the fan clutch fails, it creates a massive rotating imbalance that shakes the entire front end when revved.
The flexplate connects the engine to the transmission's torque converter. If it cracks around the mounting bolts (sometimes due to improper torque during a transmission swap), it causes severe vibration and a loud rattling noise when revved.