* Transmission Fluid Level and Condition: This is the first thing to check. Low fluid level will cause all sorts of shifting issues. Dirty or contaminated fluid can also severely impact transmission performance. Check the fluid level with the engine running and warmed up. The fluid should be bright red; dark brown or burnt smelling fluid indicates a serious problem.
* Transmission Solenoids: These electro-magnetic valves control fluid flow within the transmission, dictating gear changes. A faulty solenoid can cause erratic shifting, inability to upshift, and the RPM fluctuations you're experiencing.
* Transmission Valve Body: The valve body houses the solenoids and other internal valves that regulate fluid pressure and shifting. Internal wear or damage within the valve body can cause similar symptoms.
* Torque Converter: This component connects the engine to the transmission. A failing torque converter can cause slippage, resulting in high RPMs and poor shifting. This is less likely to cause downshifting issues, however.
* Governor: The governor controls shift points based on vehicle speed. A malfunctioning governor could lead to improper shifting.
* Shift Linkage (if applicable): Older vehicles might have a mechanical linkage connecting the shifter to the transmission. A problem with this linkage could prevent proper gear selection. However, this is less common on automatics of this era.
* Computer Control Issues (PCM/TCM): The Powertrain Control Module (PCM) or Transmission Control Module (TCM) (these might be combined in your vehicle) controls the transmission's operation. A faulty module can lead to erratic shifting patterns. This is harder to diagnose without diagnostic tools.
What you should do:
1. Check the transmission fluid level and condition immediately. This is the easiest and cheapest check, and it could solve the problem.
2. If the fluid is low or dirty, have it changed and the filter replaced. This is a relatively inexpensive repair.
3. If the problem persists, a professional mechanic needs to diagnose the issue. They'll likely use a scanner to read trouble codes from the PCM/TCM and perform further tests to pinpoint the exact cause. It's best to specify the symptoms you've described to the mechanic.
Ignoring transmission problems can lead to catastrophic and expensive damage. Don't delay getting it checked.
