A/C Idle Up

[PhoenixRPR]

For my 1992 Eclipse GSX, I want to know which components are involved that make the car idle up appx. 100 rpms when the A/C is turned on. This is the way the car is designed, but when I turn my A/C on, it bogs down several hundred RPMs. I replaced the ECU, but that did not fix the problem.

Thanks!

 

[olmytsi]

Good question. I am also interested in this.

 

[PhoenixRPR]

Thanks. I hope more people buzz in here.

 

[PhoenixRPR]

I just realized I should note that my Idle Speed Controller (ISC Motor) is functioning properly in all other instances.

 

[steve]

There isn't much to it. The ECU gets a signal that the AC is on and it steps the ISC out to raise the engine speed. The other sensor involved is the IPS.

You need to measure the ISC coil resistances and check the IPS and AC inputs to the ECU.
If you had a bad ISC with a shorted winding it doesn't take more than a few milliseconds to pop the driver in the ECU so what might have been a good ECU can quickly become a bad one.

Steve

 

[PhoenixRPR]

Could explain the IPS sensor a bit more. Idle Position Sensor? Is there a good way of checking that the IPS sensor is good other than the fact that my car idles fine except when the A/C is on?

I will have the ISC checked out again, but I've checked the resistances a little while ago and they were within range and the motor was stepping 0-120 correctly, except when the A/C was involved.

 

[steve]

The ECU has a pullup on the Idle Position Sensor pin 14 to 12v. When the IPS is closed it grounds the pin pulling it close to 0v. With the throttle open the pin rises to 12v.


Steve

 

[Judacoth]

Pin 14 is the air flow sensor active filter reset (idle switch). I do not see the bearing this has on your a/c idle up problem.

 

[steve]

Pin 14 is the air flow sensor active filter reset (idle switch). I do not see the bearing this has on your a/c idle up problem.

It's the Idle Position Switch on 91+ ECUs and MAF reset on '90 ECUs. (The pins switched between 90 and 91)
The logic for AC idle up only applies if the ECU thinks the throttle is closed. So it's one of the things to check.

Steve

 

[PhoenixRPR]

We checked out Pin 14 on the ECU and it's not malfunctioning. So the IPS is out of the equation.

 

[94EclipseGST]

I had this problem. This and all other idle and surge problems went away when I replaced the FIAV.

 

[PhoenixRPR]

I had this problem. This and all other idle and surge problems went away when I replaced the FIAV.

Can you go into detail about this procedure? (include part numbers) Thanks!