* Transmission Problems: This is a very common cause. A 1987 LeSabre likely has an automatic transmission, and several issues can cause jerking:
* Low Transmission Fluid: Check the fluid level and condition. Low fluid or fluid that's dark, burnt, or smells bad indicates problems.
* Worn Clutch Packs: These are responsible for engaging the gears. Wear causes slippage and jerking.
* Solenoid Problems: These electrically controlled valves direct fluid flow within the transmission. A faulty solenoid can cause erratic shifting.
* Valve Body Issues: The valve body controls the transmission's operation. Internal wear or blockages can cause shifting problems.
* Torque Converter Issues: This component connects the engine to the transmission. Problems can cause slippage and jerking.
* Ignition System Issues:
* Worn Spark Plugs or Wires: Misfires caused by worn plugs or wires can lead to jerking, especially under acceleration.
* Distributor Cap and Rotor Problems: These components distribute the spark to the plugs. Cracks or wear can cause misfires.
* Ignition Coil Problems: A failing coil can weaken the spark, leading to misfires.
* Fuel System Issues:
* Clogged Fuel Filter: A clogged filter restricts fuel flow, leading to hesitation and jerking.
* Fuel Injectors (if equipped): Clogged or faulty injectors can cause inconsistent fuel delivery.
* Fuel Pump Problems: A weak or failing fuel pump may not deliver enough fuel under acceleration.
* Engine Problems:
* Vacuum Leaks: Leaks in the vacuum system can disrupt engine timing and cause erratic performance.
* Carburetor Issues (if equipped): Problems with the carburetor's jets, float level, or other components can cause inconsistent fuel delivery.
* Drive Shaft or Axle Issues: Although less likely to cause jerking *specifically* during acceleration, worn or damaged components in the drivetrain *could* contribute to a rough or jerky feel.
Troubleshooting Steps:
1. Check the transmission fluid: This is the easiest and cheapest thing to check first.
2. Check for any visible issues: Look for obvious signs of leaks, damage, or worn components under the hood and underneath the car.
3. Listen to the engine: Pay attention to any unusual sounds like knocking, squealing, or rattling.
4. Get the codes read: If the car has a check engine light, get the diagnostic trouble codes (DTCs) read using an OBD-I scanner (for a 1987 model). This might give you a clue.
Given the age of the vehicle, it's highly recommended to have a qualified mechanic diagnose the problem. Many of these issues require specialized tools and knowledge to pinpoint and repair. Ignoring the problem could lead to more significant and costly damage.
