* Transmission Problems: This is a strong possibility. The shuddering could indicate worn clutch components (if it's a manual transmission), low transmission fluid, problems with the torque converter (if it's an automatic), or internal transmission damage. A low or dirty transmission fluid is a common cause and should be checked and changed first.
* Engine Issues: A misfire in one or more cylinders can cause rough running and poor acceleration. This could be due to faulty spark plugs, ignition coils, or a problem with the fuel system (e.g., clogged fuel filter, fuel injectors).
* Drivetrain Problems: Worn motor mounts or transmission mounts can allow excessive movement, leading to vibrations felt throughout the car. Problems with the CV joints or axles (especially if the shudder is more pronounced during turns) can also cause vibrations. A failing differential could also contribute, though less likely to be the primary cause of slow acceleration.
* Wheel Balance/Alignment: While less likely to cause the slow acceleration, unbalanced or misaligned wheels could contribute to the shaking sensation.
What to do:
1. Check the Transmission Fluid: This is the easiest and cheapest thing to check first. If the fluid is low, dirty, or burnt, it needs to be replaced. Consult your owner's manual for the correct type of fluid and procedure.
2. Check the Engine: Listen carefully for any unusual noises coming from the engine. Take note of whether the shaking is consistent across all gears or more pronounced in specific gears. Have a mechanic check for misfires using diagnostic tools.
3. Professional Diagnosis: Because several components could be the cause, it's best to take your Focus to a qualified mechanic for a proper diagnosis. They can perform a thorough inspection and pinpoint the exact problem, saving you time, money, and potentially further damage.
Don't continue driving the car extensively with this problem, as it could worsen the underlying issue and potentially cause more significant damage to your transmission or engine.
