Need help with AC idle circuit. - 3000GT/Stealth International Message Center

Hammer · 07-07-2008, 06:29 PM

I have a new idle problem.
When I turn my ac on manually idle works fine.
When I use the automattic setting and set a temp on the climate control
idle works fine as long as the ac is working hard.

When the car cools off inside then the fan speed slows down and the ac
comes on intermittent to keep the car cool. It is in this mode when the idle
no longer holds. Car will idle fine at a stop then the ac kicks in and the idle
drops and the car dies. I think the ISC is good. I think the problem is in what
ever device sends a signal to the ISC that the AC is on. That part works fine
when the ac is turned on manually but fails during the climate control auto mode when ac is not working hard.

Anyone with an idea where to look?

Hammer · 07-08-2008, 03:18 PM

I did more tests today.
With the climate control off the engine idles at 800 RPM.
With the climate control in AC mode the engine idles at 1100 RPM.
With the climate control in AC ECON mode the engine idles at 600 RPM
rough idle and dies after a bit.
With the climate control in AUTO mode and the ac running only occasionally
the engine idles at 600 RPM rough idle and dies.
With the climate control in AUTO mode and the ac running full blast the engine
idles at 1100 RPM fine.

So why the difference in idle? I thought the ac is either on or off acording to the ECU and the signal the ECU sends to the ISC is based on if the ac is on or off. For some reason my ECU thinks the ac is off when it is in ECON mode
and sets the idle to 800 RPM but I am assuming the load of the ac drags the idle down to 600 and causes the rough idle and eventually the engine dies.

How do I fix this?

07-07-2008, 06:29 PM	#1 (permalink)
Hammer Hammer Join Date: Apr 2007 Location: Grand Forks ND Drives: 95 3000gt vr4 stock Trader Rating: (1)	Need help with AC idle circuit. I have a new idle problem. When I turn my ac on manually idle works fine. When I use the automattic setting and set a temp on the climate control idle works fine as long as the ac is working hard. When the car cools off inside then the fan speed slows down and the ac comes on intermittent to keep the car cool. It is in this mode when the idle no longer holds. Car will idle fine at a stop then the ac kicks in and the idle drops and the car dies. I think the ISC is good. I think the problem is in what ever device sends a signal to the ISC that the AC is on. That part works fine when the ac is turned on manually but fails during the climate control auto mode when ac is not working hard. Anyone with an idea where to look?

07-08-2008, 03:18 PM	#2 (permalink)
Hammer Hammer Join Date: Apr 2007 Location: Grand Forks ND Drives: 95 3000gt vr4 stock Trader Rating: (1)	Re: Need help with AC idle circuit. I did more tests today. With the climate control off the engine idles at 800 RPM. With the climate control in AC mode the engine idles at 1100 RPM. With the climate control in AC ECON mode the engine idles at 600 RPM rough idle and dies after a bit. With the climate control in AUTO mode and the ac running only occasionally the engine idles at 600 RPM rough idle and dies. With the climate control in AUTO mode and the ac running full blast the engine idles at 1100 RPM fine. So why the difference in idle? I thought the ac is either on or off acording to the ECU and the signal the ECU sends to the ISC is based on if the ac is on or off. For some reason my ECU thinks the ac is off when it is in ECON mode and sets the idle to 800 RPM but I am assuming the load of the ac drags the idle down to 600 and causes the rough idle and eventually the engine dies. How do I fix this?

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