The accumulation of moisture at major connectors and control units can cause various ABS/PDAS faults due to corrosion.
Problems for specific Porsche 911 Turbo years:
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Newest reported 1991 Porsche 911 Turbo problems
Check Engine Light illumination and performance issues can be caused by oxygen sensor faults.
An accumulation of small air leaks at various locations around the intake manifold/intercooler area can cause performance problems.
An external fluid leak may develop at the pressure switch; fluid will be evident in the trunk and the reservoir level will drop.
The hydraulic pump relay can fail, causing the pump to run continuously, which leads to hydraulic pump failure due to overheating. Incorrect pressures will cause a low brake pedal or a high pedal effort with the possibility of other strange symptoms.
Pay close attention to warning lights and have the brakes inspected regularly—immediately address any brake problems. Hard driving habits will cause excessive brake pad and rotor wear. Aged brake fluid can cause numerous problems, including "waxy" buildup visible in the reservoir, so replace the brake fluid regularly. Special procedures are required to bleed/flush ABS pump.
Engine issues related to valve guide wear are common. Oil consumption, smoking at first startup, and valve train noise are all symptomatic of loose guides and worn valve stems. The valve train is complex and should be thoroughly inspected if a problem arises. Worn turbocharger bearings can also be a component in engine oil consumption.
Over time, the engine can leak oil at various locations. Early-production vehicles require engine disassembly and modification to resolve leaks at the cylinder heads, oil return tubes, valve covers, timing covers, chain housings, case through bolts, and lines to/from the oil cooler.
Pay close attention to secondary ignition system components (distributor caps, rotors, cables, and connectors).
If the engine won't turn over or cuts out at seemingly random times, it may be a failing relay for the DME system.
The brake warning display and warning gong can activate, typically after the first start of the day. The warning light/gong might stop after idling for a short time. This fault is usually caused by low stored hydraulic pressure due to a failed high pressure accumulator.