924Board.org

[stevekat]

I've read most of what's been written on the systems on the 81 S2 cars. While I shall probably dig in looking for vacuum leaks, AAV, measuring WUR if need be, my symptom is relatively straightforward from an effect standpoint, so I wanted to pose it here before heavy lifting, in case someone can nail it for me, from past experience.

Car starts, cold, warm hot, anytime, no problem. Cold or hot, idle starts around 1200 rpm or somewhat higher, and depending on initial temperature, eventually (minutes, sometimes many, but not seconds) the idle shall drop to 900 and then about 550, in two apparent steps, seemingly related the heat of engine. When she is idling above 550 (ie: 900 or 1200) she has some hesitation - bogs or has low power until hitting boost. Drivable, just a pain. When the idle gets down to 550 on its own, system seems nominal, good response down low, and she runs well through all rpm ranges.

Thought this might make a bulb go off in the collective memory banks.

AAV, temp sensor, pressure to DITC, WUR, whatever. I am thinking it might be a single point of failure - but realize it could be 'other'

Has a CGT intercooler.

[924RACR]

Yeah, so isolate and fix those leaks, then doublecheck the idle settings (idle speed/timing, and then mixture).

Took me a LONG time of driving and fixing before I got all of mine.

Still have the high idle when starting - particularly when warm - that goes away within a minute, but I believe this is normal, part of the programming.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[stevekat]

Started yesterday at 10:00AM, finsihed at 10:30PM, replacing all elbows, taking out and cleaning AAV (was pretty clean) replaced Decel Valve since I had a spare, replaced all vacuum lines but one or two. Replaced all elbows but the one underneath near the turbo (shall do that another day.) I didn't have Porsche cloth braided smaller diameter vacuum lines, but did have the larger diameter. Clamped all lines. Very hard to find clamps for the small lines. Huge difference when done - however not sure it was all due to the new rubber.

The smaller diameter elbow going to the Decel valve was plugged with some kind of cap inside - jeeesh. Not sure if this was added to solve some running problem the prior tech/owner could not otherwise resolve, or due to an effort to supposedly aid performance (car has CGT intercooler.)

When first took her out, hesitation was gone, however when accelerating, upon taking foot off the gas while shifting up, the rpm would continue up, ie: accel to 4000, foot off gas, shift up a gear, rpm would be +/-5000 at clutch release. RPM would come down if just took foot off gas, and coasted after a couple of seconds, and if one was not accelerating, just driving, and changing gear, rpm would not rise, but would not fall quickly. Assume this was related to timing/idle set/mixture.

Did a quickie adjustment without the timing step (mixture and idle) and seems much better. On accel, rpms now don't rise after clutch in, but don't come down much in the quick interval before shifting. Drivability is incredibly enhanced overall.

[Smoothie]

The now-working decel valve accounts for the delay in rev-drop between shifts. That's its' job of course.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[924RACR]

Cool... if you get the timing light out and really set the idle, that might further help the rev drop issue...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype