1. Engine Mounts:
* The most likely culprit: Worn or broken engine mounts allow the engine to vibrate excessively, particularly when the car is idling.
* What to look for: Visual inspection for cracks, tears, or excessive movement in the engine mounts.
* How to fix: Replace the engine mounts.
2. Idle Air Control (IAC) Valve:
* How it works: The IAC valve controls the amount of air entering the engine at idle, helping to keep the engine running smoothly.
* Why it might be the problem: A dirty or faulty IAC valve can cause erratic idle speeds and shaking.
* What to do: Clean the IAC valve or replace it if necessary.
3. Fuel System:
* Potential issues: A clogged fuel filter, low fuel pressure, or faulty fuel injectors can cause the engine to run rough, especially at idle.
* What to check: Inspect the fuel filter and have fuel pressure checked by a mechanic.
4. Vacuum Leak:
* How it affects things: A vacuum leak allows unmetered air into the engine, disrupting the air/fuel mixture and leading to rough running.
* How to find it: Listen for hissing sounds around the intake manifold, vacuum hoses, and other components. Use a vacuum gauge to check for leaks.
5. Ignition System:
* Even after changing plugs: While you've addressed spark plugs, other ignition components like spark plug wires, ignition coils, or the distributor cap (if applicable) could be faulty.
* What to check: Inspect the wires for cracks, wear, or loose connections. Test the ignition coils for proper function.
6. Other Considerations:
* Engine temperature: A cold engine might shake more until it warms up.
* Transmission: Some automatic transmissions exhibit slight vibration during gear changes.
* Wheel balance/alignment: Unbalanced wheels or misaligned tires can cause shaking, but typically at higher speeds.
Recommendation:
* Start with a visual inspection: Check engine mounts, hoses, and connections for obvious issues.
* Get a professional opinion: If you're not comfortable with the diagnosis, take it to a trusted mechanic. They can use diagnostic tools and test equipment to pinpoint the root cause.
Remember, properly diagnosing the issue will lead to the most effective solution. Let me know if you have any more questions or would like to go into further detail about any of these potential causes.
