* Faulty Trunk Release Mechanism: The most common culprit. The internal latch mechanism can become worn, sticky, or misaligned, causing it to release unexpectedly. This could be due to age, rust, or corrosion. The cable itself might also be frayed or sticking.
* Loose or Damaged Trunk Release Cable: The cable connecting the interior release button (and possibly the key cylinder) to the latch can stretch, become disconnected, or simply be rubbing against something, causing it to snag and release.
* Electrical Issues (Less Likely): While less common on older cars without extensive electrical systems in the trunk, a short circuit or faulty wiring related to the power trunk release (if equipped) could potentially cause the latch to disengage. This is more likely if the trunk only pops open when the car is running.
* Vacuum System Issues (Possible, depending on model): Some older cars used vacuum systems to assist with the trunk release. A leak in the vacuum lines or a malfunctioning vacuum pump could potentially lead to unintended trunk opening. This is less probable but worth considering.
* External Force (Least Likely): While unlikely to cause repeated popping, an impact to the rear of the car or a significant jarring could potentially cause the trunk latch to disengage.
Troubleshooting Steps:
1. Inspect the Trunk Latch Mechanism: Carefully examine the latch assembly for any signs of damage, rust, or misalignment. See if you can manually manipulate the latch to see if it's binding or sticking.
2. Check the Trunk Release Cable: Trace the cable from the interior release to the latch. Look for fraying, kinks, or areas where it might be rubbing against the car's body.
3. Test the Trunk Release Button and Key: See if the trunk releases consistently when using the interior button and/or the key. Inconsistent operation points towards a problem with the cable or latch.
4. Inspect Wiring (If equipped with power trunk release): If your model has a power release, check the wiring harness for any damage, loose connections, or corrosion.
If you're not comfortable working on the car yourself, it's best to take it to a mechanic. They can diagnose the problem accurately and perform the necessary repairs. They may also have access to parts that might be difficult to find for such an older vehicle.
