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04 Cayenne TT – High Idle and Brake Booster Failure after replacing co

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Long time lurker (these boards are so helpful) but I've finally run into something worth posting about. Last week my coolant Ts at the back of my 04 Cayenne Turbo started leaking. I've already got the metal pipes between the thermostat and bracket, but the Ts weren't changed to metal and cracked (car has about 80k miles on it now). Lots of steam and a visible spray from the fitting where the smaller turbo T connects to the larger T. For a second I thought the car was definitely on fire.


Ordered new Ts with metal pipes, took the intake and manifold off no sweat, and got the metal Ts with new tubes installed after weekend's worth of effort. While I had the throttle body off I gave it a cleaning since it was covered in some oil, and I replaced the intake plenum Y in front of it since I suspected a crack was forming at the seam in the front. I also installed new manifold gaskets and throttle body gaskets. I thought for sure I would break the plastic vacuum T everyone talks about at the back against the firewall, but that was fine, and none of the PCV hoses running over the V were cracked or overly brittle. I also replaced the PCV check valve since I've been meaning to do it and had that part handy (I wanted to do AOS too but that cap is really glued on there). 


However next time I started the car up to fill and bleed the coolant system I got a weird high idle (1.1k RPM) that fluctuates, and a bunch of codes about the throttle position calibration not finishing. After a test drive I immediately noticed braking performance was reduced too, followed by the brake booster failure message. 


Obviously at this point I suspect a vacuum leak somewhere in one of the dozen hoses, but I'm not sure what to start. I'm suspecting the brake booster vacuum pump and hose bracket might have a leak that I exacerbated while taking the torque arm out, and really hoping that the lines at the back of the intake manifold aren't leaking now. I thought the brake booster vacuum was controlled via the pump on the passenger side. 


I saw the following codes:


P1535 Throttle adjust unit (test aborted due to violated ambient condition)

P0507 Idle air control system RPM – upper limit value exceeded

P2220 Throttle actuator control system – sudden airflow detected 

P1455 Brake booster system implausible signal 

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Just to update, I fixed it and figured everything out. 


Throttle body needed to be re-calibrated which I performed with durametric. For some reason the 60 seconds in on position and 10 seconds of off didn't do it. No matter, it only took a few seconds to run the adaptation over the computer, then the idle came back down.


Brake booster was equally simple. I forgot to plug the vacuum pump back in. Plugged it in, reset codes, brakes are back and the Cayenne runs great now. 

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