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bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

I've recently adjusted my idle fuel mixture to where it should be (13s-14s) as it was way too rich before, and then adjusted my idle down as far as I could, which is still about 1050 with the car warmed up. However, I've noticed that when I cold start now, it starts fine but then idle gets really rough and if I don't give it some gas, it will die. If I do this for a minute or two and then drive it's fine.

Does this sound like a Auxiliary Air Valve problem? I've read that they usually fail stuck open, which sounds like it would be the opposite of what I'm seeing. Although, as I mentioned, I couldn't get the idle under 1000 (warmed up) so maybe it is stuck open, and to compensate I cranked the idle screw setting too tight?

Everything else seems really good right now...boost enrichment is happening as it should, etc.
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1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

MOTANUL · Joined: 19 Nov 2018 Posts: 214 Location: ROMANIA BUCHAREST

Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

Mine idles higher and richer when first started cold...... idle reduces and AFR leans slowly as it warms up. I don't run the CSV so its all controlled via the AAV opening up.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

Are you running your stock lambda system with the narrowband sensor at all?
If so.. You should set your idle AFR with the dwell meter method and not by a wideband reading..

Otherwise, too high of an idle sounds like a sticky aav, decel valve, or post TB vacuum leak..
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80 Turbo - Slightly Modified

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

I disconnected the O2 sensor to get rid of rhythmic surging at cruise, and then replaced it with my wideband. I was going to try connecting the narrowband emulator signal but never got around to it. Not sure it's needed?

I definitely need to take a closer look at the AAV. I don't know anything about a decel valve but I will learn about it. Vacuum leak is certainly possible, although when I smoke tested it a while back I didn't find one. I should probably give that another try.

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

The AAV closes as it heats up, right? Or do I have that backwards?

It might actually be my cold start valve? Maybe? I say that because for once my AFM worked from startup, and my idle ratio was way lean as it was running poorly, and then as it warmed up, the ratio at idle ended up back where it belongs.
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1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

MOTANUL · Joined: 19 Nov 2018 Posts: 214 Location: ROMANIA BUCHAREST

From what I remember at NA it closes. Closes in about 1 minute. And it stays close as long as the ignition is on (warm engine).

I noticed that the AAV turbo shape is a little different - I did not study at all if it differs in terms of operation.

I have a S1 Porsche turbo (no O2 senzor or lambda). The idle is 900 rpm when cold and 1050 rpm when warm.
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1980 Porsche 924 Turbo (931) diamond silver metallic/helios blue metallic
sold Porsche 924 NA 1979

kondzi · Joined: 02 Jul 2018 Posts: 485 Location: Poland/EU

931 EU / S2 - AAV closes when warming up. Have Innovate AFR and it shows that when heating AFR gets leaner at idle. With AAV closing, RPM goes down. My issue is my AAV is not closing smoothly, and when engine warms up, the idle goes higher (stuck AAV), sometimes up to 1600-ish RPMs. Then I use the wooden part of the hammer, knock few times on the AAV and RPM drops.
The other thing that can impact idle RPM is ignition advance angle. Take a look if it’s working correctly.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)