4 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHIntermittent Idle Issue ? Porsche 996
Reported or suspected cause
so intermittent
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
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Reported cause · Original poster
I�m getting really frustrated because the issue is so intermittent.
Leading evidence: 'so intermittent' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'so intermittent' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check live signals of sensors and actuators' (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 · Original poster
I already tested the ICV electrically and also checked the RPM response with the A/C on, and both tests were normal.
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Performed · outcome unconfirmed · Original poster
● Cleaned/replaced the idle control valve (Leerlaufregler)
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4 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Hi everyone,
I�m having an intermittent idle issue with my Porsche 996. Year 1999 model C2 cab. Cable throttle.
Sometimes the idle gets stuck around 1,300�1,500 rpm, especially when the engine is warm. Sometimes the RPM also drops very slowly after revving. Also it then idle hunts.
The strange thing is that the problem is not always present. If I switch the engine off, wait around 10�15 minutes, and restart it, the idle can be completely normal again.
I�ve also noticed that, when the problem occurs, the exhaust sometimes sounds different from side to side. One exhaust outlet can sound noticeably louder than the other, or the exhaust note seems uneven between the two sides. I�m not sure whether this is related, but it may be another useful symptom.
So far I have already:
● Replaced the MAF/LMM
● Cleaned/replaced the idle control valve (Leerlaufregler)
● Replaced the Lambda sensors
● Replaced the EVAP/purge valve
● Performed a smoke test of the intake system
● Fixed the vacuum leaks I was able to find
● Checked the throttle body
● Checked for obvious intake/vacuum leaks
● The car sometimes runs perfectly for an entire day, then the problem suddenly returns
I�m getting really frustrated because the issue is so intermittent.
What would you check next?
Could this be related to the crankcase ventilation (AOS/PCV), throttle body, fuel pressure, or something temperature-related?
Any ideas or similar experiences with a 996 would be greatly appreciated.
Sounds like ICV to me, even if you have cleaned it. Did you check whether it opens and closes when connecting the middle pin to ground and either outer terminal to +12V for 0.2 sec?
Do the revs increase for a moment when the engine catches upon starting and then drop down to idle rpm? Then ICV is most probably fine. Another quick check is the presence of a slight rpm increase at idle when switching on the A/C.
Changing rpm due to AOS failing is not something I recall but if you still have a vacuum leak then possible) but test if it is hard to undo the oil filler cap when the problem occurs. If yes, this indicates that the AOS is not OK. Unfortunately this test is only conclusive if you don't have a vacuum leak you haven't found yet.
I don't know if an NOK working vario cam solenoid can lead to your observations but different exhaust notes between both banks can only be explained by them as they are the only thing that controls a whole bank and there is one for each bank, whereas of the 'rest' either one or six items exist.
Apart from cam sensors (if not M96.01), lambda and knock sensors of which there are 2 and they're bank specific.
Get the piwis3 for 75USD (thread on here) or Durametric to check live signals of sensors and actuators.
HTH.
Edit: it is entirely possible that the outer sheath of the throttle cable drops out of its seat thereby preventing the throttle from completely closing.
Thanks for the suggestions. I already tested the ICV electrically and also checked the RPM response with the A/C on, and both tests were normal.
Yesterday I measured the crankcase pressure with the engine fully warm through manometer with a modified oil filler cap. The gauge showed +0.05 bar (around +20 inH₂O) with the hose from the manometer connected to the negative port. That does seem very high so I don�t quite believe it. So by that reading the aos must be blocked. Is that even possible?
The oil filler cap has a noticeable vacuum when the problem occurs. But not to strong.
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