16 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCH?Bouncing? idle
Reported or suspected cause
aos, changed it out and, voila
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
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Reported cause
Experienced the identical symptom with my 1999 996 C2, it was the AOS, changed it out and, voila, no more bouncing idle.
Leading evidence: 'aos, changed it out and, voila' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'aos, changed it out and, voila' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check first' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
In trying to fix it I changed the plugs, coils, AICV, some sensors, cleaned the throttle body, etc.
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Performed · outcome unconfirmed
In the end mine was corrected when I replaced the AOS when my clutch went.
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Suggestion
I would replace the AOS proactively,, Mine was tested at the last oil change, and shortly before the next oil change it failed, gulped oil and broke the #1 cylinder.
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Rennlist: 1 discussions
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Generation: 20261026T213932Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
I�m experiencing a �bouncing� idle and wondered if anyone has an idea. It just showed up a couple days ago. It�s intermittent. Idle may fall to 400rpm, just short of stall, them will blip up to 800-1000rpm and repeat. Other times it may bounce from 600-800. Normal idle w/o ac is 600. With ac it�s 800. I replaced coils and plugs a couple months back. No issues. I thought the bounce might be fuel injector related. But the car runs normal under throttle and above 800rpm. No CEL.
Appreciate all thoughts.
First �issue� after 3mo of ownership and 3k miles on my 99. Was kinda waiting for stuff like this to show up. No complaints.
Your '99 has a AICV, air idle control valve. Good place to start. Remove and clean or replace.
I had a bouncing idle that was that come and go for months. In trying to fix it I changed the plugs, coils, AICV, some sensors, cleaned the throttle body, etc. None of that helped but that's what everyone told me to check or replace.
In the end mine was corrected when I replaced the AOS when my clutch went.
^ Correct. On a 99 that idle control valve is the place to check first. Remove TB and remove the ICV from the TB. Clean with alcohol and Q-tips. Cycle the valve with a 9V battery. It will look black inside and once cleaned it will be shiny silver inside. Be very careful of the ICV gasket. It is very fragile.
Cleaned the idle valve and throttle body. Went to reinstall the TB and barely bumped the plastic coolant hose connector to the oil separator. The cheap plastic hose connector snapped and coolant sprayed everywhere. There�s a good reason for the aftermarket steel connector. First pic show the upper hose with the male attachment still inside.
20yr old plastic gets brittle. Two male ends for this connector. One end is still attached to bottom hose to oil separator. Other end is inside the upper hose.
Worth it. Found it for $38 elsewhere.
Nope.
Not sure if you purchased that part yet, but this one is aluminum, less expensive, and looks OEM.
https://www.rockauto.com/en/catalog/.../+flange,11566
I suspect after 20 years the AOS should be replaced. Not seeing any blue smoke or oil in the intake plenum. Before I tackle the AOS I�ll most likely get readings from a manometer.
idle hasn�t occurred in a couple weeks. Stopped even before I cleaned the TB. Tired itself out maybe??? Doubt it. Expect it will return at some point. AOS is coming into view.
I would replace the AOS proactively,, Mine was tested at the last oil change, and shortly before the next oil change it failed, gulped oil and broke the #1 cylinder.
Vacuum leaks are one of the most common causes of run-ability issues on all cars..
I compare it to a BMW E46 cooling system,, every 7 years or 80K the ENTIRE cooling system
and all the hoses, plastic pipes, pump, radiator all of it is a service item.. You can skip it but WHEN the
expansion tank slplits or the radiator neck falls off it empties the engine in about 1 second,
and your running dry at full temp. its a 2200 to 2800 dollar adventure.. less at a indy more at the dealer.
If it blows there is about a 75% chance its a full rebuild on the engine.. YMMV!
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