A/C load drags down idle - how to adjust?

[e p slick]

A/C load drags down idle to stall range - how to adjust? I just added A/C to old 86 Carrera and am not entirely sure how to compensate for A/C load at idle. Car sometimes stalls with A/C on and quick lift off accelerator pedal. I have had simple CIS cars but now Motronic. Have read some slightly conflicting adjust procedures in Bentley and Bosch books and now ask if anyone can suggest simple fix. Appreciate any input.

EP Slick - Tucson

[T77911S]

the idle control valve should do it. check to see if it is sticking.

[Steve@Rennsport]

Hi Paul,

You'll need to do some detective work in the shop manuals, but you need the connection between the compressor clutch and the ECU.

This tells the ECU to raise the idle speed via the ISV when the compressor clutch is engaged.

[e p slick]

Thanks everyone. Idle valve seems to work properly per suggested testing. I have apparently bypassed ECU circuit with auxiliary wire so Steve, your adivce is most likely what I needed to pursue solution.

Again, Thanks All

EPS

[86 911 Targa]

Originally Posted by e p slick

A/C load drags down idle to stall range - how to adjust? I just added A/C to old 86 Carrera and am not entirely sure how to compensate for A/C load at idle. Car sometimes stalls with A/C on and quick lift off accelerator pedal. I have had simple CIS cars but now Motronic. Have read some slightly conflicting adjust procedures in Bentley and Bosch books and now ask if anyone can suggest simple fix. Appreciate any input.

EP Slick - Tucson

I'm working this identical issue with another P-member who works on DME's.

I went through all of the Bentley diagnostics, ICV, Idle switch, and still have the issue.

The idle is rock solid at 800 rpm's w/o A/C.

With A/C, the idle drops down to about 750, then oscillates
between 650-750 rpms.

Your DME needs 12v on pin #29 when you activate the A/C
(pages 970-49 and 970-28).

This will provide an increase in rpm's.

But first, perform the ICV/Idle position switch diagnostics.

Please let us know how things work out.

Good luck,

Gerry