What are the common issues with the all-wheel drive system on the 1990 Porsche 911 Carrera 4 that I should be aware of when considering purchasing one?

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Based on my research on the 1990 Porsche 911 Carrera 4 (964) all-wheel drive system, here are the common issues to be aware of:

**Primary AWD System Concerns:**

1. **AWD/ABS Warning Lights** - This is the most frequently reported issue. The dashboard warning lights for both all-wheel drive and ABS systems can illuminate, often due to:
   - Faulty wheel speed sensors
   - Issues with the control module communication between AWD and ABS systems
   - Sometimes the lights come on intermittently and the car drives normally, other times it affects performance

2. **Viscous Coupling Issues** - The heart of the AWD system:
   - Can fail over time, especially if not properly maintained
   - Symptoms include unusual noises from the center differential area
   - Replacement is expensive (typically $3,000-5,000 parts and labor)

3. **Front Differential Problems**:
   - Oil leaks from seals are common
   - The front differential requires specific fluid changes
   - If neglected, can lead to premature wear and expensive repairs

4. **System Complexity** - The 964 was Porsche's first modern AWD system:
   - More complex than later systems
   - Requires specialized knowledge for proper diagnosis
   - Parts can be expensive and sometimes hard to find

**Pre-Purchase Inspection Recommendations:**
- Have a Porsche specialist scan for any AWD/ABS fault codes
- Check service records for front differential fluid changes
- Test drive to feel for any binding or unusual behavior in tight turns
- Listen for unusual noises from the center differential area

**Good News:** When properly maintained, these systems are quite reliable. Many owners report trouble-free operation for high mileages with regular maintenance.

Lot P-3144: 1990 Porsche 911 Carrera 4

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Lot P-3144: 1990 Porsche 911 Carrera 4

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