* Torque Converter Clutch Problems: This is the most probable culprit. When idling, the torque converter is essentially "locked up" and any imperfections, wear, or contamination within it (e.g., worn clutch plates, low transmission fluid, debris) will cause vibrations felt as a shudder. When you accelerate, the torque converter unlocks and the shudder disappears because the hydraulics are working to transmit power differently.
* Low Transmission Fluid: Low fluid level can lead to insufficient lubrication, causing the components within the transmission, including the torque converter, to rub and create shuddering. Check your transmission fluid level (using the dipstick when the engine is running and at operating temperature). Low fluid also indicates a potential leak, which needs addressing.
* Contaminated Transmission Fluid: Old, dirty, or burned transmission fluid loses its lubricating properties and can cause the same problems as low fluid. The fluid should be a reddish-pink color; if it's dark brown or smells burnt, it needs to be replaced.
* Torque Converter Solenoid Issues: These solenoids control the engagement and disengagement of the torque converter clutch. A faulty solenoid can cause erratic behavior, leading to shuddering at idle. This is less likely than the issues above, but possible.
* Transmission Mount Problems: While less likely to only manifest at idle, a worn or damaged transmission mount could contribute to vibrations that feel like shuddering. Inspect the transmission mount for any signs of damage or wear.
* Other Internal Transmission Problems: In more severe cases, internal transmission problems, such as worn planetary gears or other internal components, could contribute to this symptom. However, these problems usually cause other symptoms (like slipping or hard shifting) in addition to the idle shudder.
What to do:
1. Check the transmission fluid: This is the first and easiest step. Check the level and condition of the fluid. If it's low, dirty, or burnt, a fluid change is necessary. This might resolve the issue, but if not, further investigation is required.
2. Consult a mechanic: If the fluid level and condition are okay, or if the problem persists after a fluid change, you'll need a professional mechanic to diagnose the problem. They have specialized tools and equipment to inspect the transmission and identify the root cause, whether it's a faulty torque converter, solenoid, or more serious internal damage. They can perform a thorough inspection and provide an accurate diagnosis and repair quote.
Ignoring the problem can lead to more serious and costly transmission damage, so it's best to address it promptly.
