Transmission Related:
* Torque Converter Issues: A worn or failing torque converter can cause vibrations, especially at idle when the engine is connected to the transmission. This is a common culprit in older vehicles. The converter might be slipping or exhibiting uneven engagement.
* Transmission Mount: A worn or broken transmission mount allows excessive movement of the transmission, leading to vibrations felt throughout the car.
* Transmission Problems: Internal transmission issues (worn clutches, low fluid, etc.) can also cause vibrations. This is less likely to be *only* at a standstill but could contribute.
Engine Related:
* Engine Mounts: Similar to transmission mounts, worn engine mounts allow the engine to move excessively, transferring vibrations to the chassis. This is a common cause of vibration.
* Uneven Combustion: Problems with spark plugs, ignition wires, fuel injectors, or the air intake system can lead to uneven combustion, causing vibrations. A misfire is a prime suspect here. You might notice a rough idle even when not in gear.
* Exhaust System: A leak in the exhaust system, especially near the engine, can cause vibrations.
* Flywheel/Flexplate: While less common, a problem with the flywheel (manual transmission) or flexplate (automatic transmission) can cause vibrations.
Other Possibilities:
* Driveshaft Issues: While less likely to be *only* at a standstill, a slightly unbalanced driveshaft could contribute.
* Low Transmission Fluid: Low fluid level can cause increased friction and vibration.
Troubleshooting Steps:
1. Check Transmission Fluid: Check the fluid level and condition. Low, dirty, or burnt fluid is a major red flag.
2. Listen Carefully: Does the vibration change with the RPM? Is there a noticeable sound accompanying the vibration?
3. Inspect Engine and Transmission Mounts: Visually inspect the engine and transmission mounts for cracks or excessive wear. Look for any movement beyond what's normal.
4. Check for Exhaust Leaks: Listen for hissing or look for signs of soot or discoloration near the exhaust manifold and pipes.
5. Scan for Codes (OBD-II): A scan tool can read diagnostic trouble codes (DTCs) stored by the car's computer, which may pinpoint the cause. Auto parts stores often offer free code scanning.
Important Note: If you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. Ignoring engine or transmission vibrations can lead to more significant and costly damage.
