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rough idle after boost and heavy braking.

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My 04 Cayenne tt runs fine, but if i boost hard then brake hard, when i come to a stop it idles rough for a few seconds then sorts itself out?

Chipped ecu, aftermarket exhaust.

Lamba on both banks good at idle and boost.

Any ideas? / help appreciated.


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Hi Loren im using a copy of Piwis tester.

Use it on all cars. System tester working fine.

If it is one of the knock-offs from China then I doubt it's accuracy.

Your symptoms say "vacuum leak" or "air intake leak" and there is always a fault or pending fault in every case I have seen.

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Thanks I appreciate your comments. Tester is perfect. Never had issues and have been using it for years. I would have expected emission faults of some description but not 1 fault logged after car plays up. I find it weird too.

I agree that it appears/sounds like a vac intake leak of some description.

Ive always seen faults logged in every other issue, but nothing. Not 1 here?

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Could be camshaft actuators..power brake veh. In drive for a few sec. Then let off... If the idle stumbles and feels like it wants to stall...then clears up..could be bank 1 or 2 actuator. If your diagnostic computer monitors camshaft angle..look at values while power braking and see if one returns to spec slower than the other..that would be the faulty actuator.

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Many Performance ECU "tunes" turn off or modify fault parameters so that certain fault warnings don't register. It's a pain to try and go back to stock software but if you have a newer OBDII flash tune (perhaps the ecu has a sticker on it denoting who tuned it) it wouldn't be that hard, if you have to remove ECU and send it out it will be a bit more time consuming and a disapointment if it doesn't change the condition or fault registering...unfortunately it's one of the "get back to basics" when trying to find cause of your symptoms. If you aren't concerned with Porsche Dealer knowing you have a tune they can flash you back to stock...

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