Vagrant77,
I am sorry I do not know where the idle speed sensor is on the 2.3 cars. I have the 2.6 m103 motor. Hopefully someone with a 2.3 can help you out soon.
Good luck with your car and by the way, ask for a Haynes manual for your car on your Christmas list. I am!!!!!!!

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1989 300CE - 269,000 km
1994 SL600 - 59,000 km