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High Idle When Warm In 3.2 Carrera

Trying to figure out what's causing the idle speed in my 84 911 to rise to 2000rpm, after the engine is fully warmed up. Prior owner's mechanic replaced the cylinder head temp sensor and also all the injectors. Starts up fine. Idle speed at startup from cold is roughly 1100rpm, then settles to 950rpm, but then increases to 2000 when the engine is fully warmed up. Where should I check for vacuum leaks? I've been told to also test or clean the Idle Control Valve?

Old 03-25-2018, 11:34 PM
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Do you have a Bentley manual? 900 is too high for base warm idle speed. I suspect vacuum leaks and idle adjustment need to be addressed. Idle control valve can be cleaned with carb cleaner.
Old 03-25-2018, 11:47 PM
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Vacuum leaks at rubber hoses and vacuum hoses behind throttle body. You can use carb cleaner or starting fluid sparingly at junctions while idle is lower, carefully, listen for a surge in rpm. It will get you close.
Old 03-25-2018, 11:52 PM
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Hi..check your micro switch on thew throttle body .. you throttle linkage has to stop on this switch ,black with red dot on top...
Ivan
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Old 03-26-2018, 03:04 AM
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+1 for the idle switch being open or not in contact.
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Old 03-26-2018, 05:18 AM
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Ok. I'll check. Is the micro switch adjustable? I do have a Bentley manual. Read through it a bit, but didn't see any mention of "high idle when warm" in the engine troubleshooting section.


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Originally Posted by proporsche View Post
Hi..check your micro switch on thew throttle body .. you throttle linkage has to stop on this switch ,black with red dot on top...
Ivan
Old 03-26-2018, 04:56 PM
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Bentley 240-21 for idle micro sw adjusting.
The sw itself is not adjustable but the linkage that engages it is.
Before that however, test to hear the click with engine off by moving linkage near throttle body, or, check Idle sw continuity at connector located near WOT sw, or, carefully depress or short the idle sw connector when running.
Yep, no hi idle prob in Table "a".
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Old 03-26-2018, 08:44 PM
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I couldn't find the para number but here is a para from Bentlley on testing the sw - you can see where it says the idle will increase by 500 over the normal idle rpm when disconnected (or if broken).
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Old 03-26-2018, 09:42 PM
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Thanks. Ran a quick check with the car cold and I do hear the switch clicking, when I move the throttle linkage. I'll check the switch with my meter to make sure it's functioning properly as well. Though doesn't it make sense that a bad idle switch would cause the idle speed to be approximately 500rpm high, regardless of the engine temperature? In my case it's rising after full warm up, but is in the 1000rpm range when the engine is cold or just starting to warm up.
Old 03-26-2018, 10:30 PM
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hi it make sense to people who know ..even to Porsche mechanics , an official book explanation....;-) trying to help you..;-) What was the last time you have checked your fuel mixture?

Ivan


???Though doesn't it make sense that a bad idle switch would cause the idle speed to be approximately 500rpm high, regardless of the engine temperature???????

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Old 03-26-2018, 11:08 PM
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