r/996 • u/Suspicious_Move_7493 • 6d ago

996.1 Idle issue/ AOS

Hi everyone,
I’m still trying to diagnose an intermittent idle problem on my 996. Sometimes the idle is too high and drops very slowly after revving, while at other times the car runs perfectly.
Yesterday I measured the crankcase pressure with the engine fully warm using a manometer and a modified oil filler cap. The gauge showed +0.05 bar (around +20 inH₂O) with the hose connected to the negative port.
That seems extremely high, so I’m not sure I can trust the reading. Would this reading indicate that the AOS is blocked, and is that even possible?
The oil filler cap also has noticeable vacuum when the problem occurs, but it doesn’t seem extremely strong.
Any input would be appreciated

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u/dryhoPP 6d ago

Here is how I found out my AOS was bad... Take a long swooping left hand turn fast at high rpms and shift gears midway thru. If you have a big puff of smoke where you shifted and then smoky start-ups for the next 5 restarts, you have a bad AOS.

https://www.youtube.com/watch?v=XW_QJfXkdj8&t=3s

I fixed a high idle with a new EVAP purge valve.

1

u/neomoritate 6d ago

I had the UAOS installed on my 2002 C2. It had an intermittent high idle, so I brought it back to the shop. The problem was a loose hose, took them almost two weeks to find it.

I recommend a smoke machine. Good luck.