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Engine stall when A/C is on. Need new Idle Control valve?

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I got a 1999 Boxster, everytime when I had the A/C turn on, the car will stall at stop light. If I rev the engine in neutual when the A/C is on, when the rpm comes back down it will drop below 600rpm and stall. I've read the DIY section about cleaning the throttle body, but my mechanic told me I probably need a new idle control valve because it control the idle when the A/C is on.

Anyone experience this before and what is the possible cause?

Thank you!


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Your mechanic doesn't quite make sense me. If it controls the idle with no ac, why not with the ac. The DME I beleive is responsible for all sorts of engine compensations. Id guess its electrical, whatever trips the DME to compensate for the a/c drag on the motor, isn't. You'd kinda halve to have a wiring diagram to figure out whats in the circut.


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You need to clean both the throttle valve and idle speed motor. The DME tries to control idle speed first by ignition timing then idle speed motor dwell.

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I wsh I could remember from 10 years ago. There was a DME reprogram for the 1999 model that staled at idle when you put the A/C on. Peter Smith did it for my 1997, but it did nothing because it was for just one model year. I also forget if the idle control valve has anthing to do with tuning the A/C on, but it would make sense because the compressor puts a load on the engine and the engine needs to speed up to compensate.

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Thanks for the advice!

I will try cleaning both the throttle body and the idle valve first before I order a new idle valve.

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