XJ XJ6 / XJ8 / XJR ( X350 & X358 ) 2003 - 2009

Restricted Performance, 2004 XJ8

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Old Jul 25, 2022 | 12:53 PM
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Default Restricted Performance, 2004 XJ8

Hi all, I have a "restricted performance" issue that has been going on for awhile now. Check engine has always been on (since I got her about 4 years ago) due to a small evap leak, restricted performance started up about a year ago - comes on after the car is on for a couple of minutes in city driving, then goes off when I get her on the interstate, then back on when slowed back down. First suspicion is a vacuum leak but haven't had any luck finding one.
Codes are: P0171, P0174, P0442 sm, P0456, and P1000. She's got just over 120,000 miles on her.
Car runs great - no performance issues other than limiting out at 3000 rpms, which is why I've let it go this long.
Any ideas are appreciated.

thanks much!
 
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Old Jul 25, 2022 | 06:26 PM
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Sounds like your small leak has increased.
After chasing mine, i found the eight gaskets.
Inside the intake manifold solved my P0171,& P0174 codes.
 
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Old Jul 25, 2022 | 10:53 PM
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Mine turned out to be an external rubber hose leaking. Took it for a smoke test, instantly the leak showed itself.
 
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Old Jul 26, 2022 | 07:13 AM
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By all means, DO eliminate any, & all other possibility's.
Before removing the intake manifold.
To replace those 8 pesky little gaskets.
 
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Old Jul 26, 2022 | 12:27 PM
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thanks, any more info on which hose and where it's located would be appreciated.
 
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