Engine Rough Running:
* Spark Plugs/Wires: Worn, fouled, or damaged spark plugs and/or ignition wires can cause misfires, leading to rough running. This is a common and relatively inexpensive place to start.
* Ignition Coil: A failing ignition coil can cause misfires in one or more cylinders.
* Fuel Injectors: Clogged or faulty fuel injectors can deliver an inconsistent fuel spray, resulting in a rough idle and poor performance.
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor provides incorrect air/fuel mixture readings to the computer, leading to rough running.
* Throttle Body: A dirty or malfunctioning throttle body can restrict airflow and cause rough running.
* Vacuum Leaks: Leaks in the vacuum system can disrupt engine performance and cause rough running.
* Engine Mounts: Worn engine mounts can cause excessive vibration, making the engine feel rougher than it actually is.
Transmission Not Shifting into 4th:
* Transmission Fluid: Low, dirty, or old transmission fluid is a very common cause of shifting problems. This is crucial to check.
* Transmission Solenoids: These control the shifting process. A faulty solenoid can prevent the transmission from shifting correctly.
* Transmission Filter: A clogged transmission filter restricts fluid flow, affecting shifting.
* Torque Converter: Problems with the torque converter can prevent proper shifting.
* Transmission Control Module (TCM): The TCM controls the transmission's operation. A faulty TCM can cause a variety of shifting problems.
* Shift Linkage/Cable (if applicable): In some older vehicles, a mechanical linkage or cable connects the shifter to the transmission. Wear or damage can affect shifting.
Interconnected Issues:
The rough running and shifting problems might be related. For example, a severely misfiring engine could cause the transmission to behave erratically or prevent it from shifting smoothly. A low transmission fluid level could also be a symptom of a larger leak that might also affect other engine components.
Troubleshooting Steps:
1. Check Transmission Fluid: This is the absolute first thing to do. Check the level and condition of the transmission fluid. If it's low, dirty, or burnt, it needs to be addressed immediately.
2. Check Engine Codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored by the car's computer. These codes can pinpoint potential problems.
3. Inspect Spark Plugs and Wires: Visually inspect them for wear, fouling, or damage.
4. Clean the MAF Sensor: Carefully clean the MAF sensor with MAF sensor cleaner (follow instructions carefully).
5. Check for Vacuum Leaks: Inspect vacuum hoses for cracks or leaks.
6. Test Drive: Pay close attention to when the rough running is most noticeable (idle, acceleration, etc.) and how the transmission shifts. This will provide valuable clues.
Important Note: If you're not comfortable performing these checks yourself, take the vehicle to a qualified mechanic. Improper diagnosis or repair can lead to further damage and higher repair costs. Ignoring transmission issues can lead to catastrophic failure.
