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Matt559
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Hi Deilenberger. First post ever! Did you replace the vacuum pump or find a disconnected pressure line? I’m having a similar issue. As my 2012 Cayenne S (958) warms up, the brake pedal sinks to the floor and becomes stiff. When this happens, the transmission no longer “automatically” upshifts gears -- yet downshifting continues to work (it refuses to shift beyond 1st gear!!!). This requires manual use of the steering wheel Tiptronic to upshift and downshift gears without an issue. This started to happen right after replacing the thermostat and water pump due to a coolant leak (big surprise…) found between the thermostat housing and left cylinder head. This required removal on the intake manifold. Running a scan with the Autel MaxiCOM MK808 revealed multiple codes including: DTC Description Status P0107 Intake manifold pressure sensor electrical fault Passive/sporadic P0660 Intake manifold switchover driver Active/static I suspect that either 1) the small vacuum line and/or wiring connector to the rear manifold valve is not connected; or 2) any other vacuum hose disconnected during manifold removal is not connected. I’ll attempt to look further to find the issue. Any suggesting to find and solve the issue? References: -Porsche 955 Cayenne Vacuum Solenoid -RennTech: stiff brake pedal - 9PA, 9PA1 (Cayenne, Cayenne S, Cayenne Turbo, Cayenne Turbo S)