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S Chassis Technical discussion related to the S Chassis such as the S12, S13, S14, and S15.

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Old 08-15-2017, 08:24 PM   #1
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s13 Single Cam KA24E Idle Issue after warmup

Hello everyone,

My brother's 1989 240sx has a strange issue at idle which I could not figure out for a decent while now. Here is what is happening: the car will start up cold and idle right at 14.7, it then richens up to about 13 until it warms up. However, once the temp gauge needle hits a certain spot in the middle, the car will go full lean and idle at like 18:1. This causes the car to sound cammed and shake around at idle and has gotten to be pretty annoying. Once the magic temperature is reached, I hear a valve open and a hissing sound start. When I unplug the yellow connector on the AAC, the car will go rich, and the hissing sound goes away. The car has all the emissions stuff behind the valve cover blocked off and unplugged.

Things I've tried:
Resealing the IACV to the intake manifold.
Sealing up some miscellaneous plugs on the manifold which I thought might be leaking.

I also tried removing the air regulator to try and reseal it. However, in doing so, one of the bolts snapped and got stuck inside the intake manifold. I looked up more information on the part and learned that it was responsible for allowing more air into the motor when the engine is cold, and closes when it warms up. My theory was that the regulator was stuck open or something and was allowing the extra air to continually flow into the manifold even when warm, causing the lean condition. So what I did was make a blockoff plate to seal the hole with some rtv and put the one bolt in and called it a day. It sealed fine but still hasn't fixed my problem.

I know there are some single cam experts out there so maybe one of you guys would be able to help me out.

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