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Discussion Starter #1
I've been tinkering with my 92 164L a fair bit during lockdown.

One thing I never liked was that the idle felt just slightly too low. Once warm it would stumble rhythmically at idle around 600-700 rpm. Within spec for my altitude but always seemed to be not enough. The charging output would waver, and it would barely hold 12v when the fan kicks on.

I didn't think there was anything wrong as it doesn't stall and it runs just fine. But I still methodically went through everything I could. Spark plugs, fuel filter, clean the AFM, clean the AIS, triple check for vacuum leaks, clean ground straps, adjust the TPS, set the throttle position, etc. Never changed anything.

Then I noticed my S25 plug (orange-red two wire plug in the front passenger footwell) was in the open configuration. This plug "tells" the ecu if the car is a manual or an automatic by either being open (no connection) or jumped (two wires connected). I wasn't sure if open was correct for a 5 speed car so I made a jumper and plugged it in.

TADA. Idle goes up 100-150 rpm. And it runs rock steady. Charging stays above 13V with fan on. Plus half a bar more oil pressure at idle.

Turns out a manual car SHOULD have the jumper in place.

I don't notice any other running/response difference, but I also have a Squadra chip and I would not be surprised if they simply put the same map on both auto/manual settings in the EPROM. A stock chip might have variations between the two settings.

So go out and check that plug if you have a manual car. If it's open, just jump the two wires together.
 

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Good to know. I never could remember was it "wit or wit out!"
 

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Discussion Starter #3
The service manual isn't super clear on it, it says the reading should be 0V with the 5 speed. What they mean is it should be shorted to ground (jumped installed).
 
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