rpm's drop with AC on?

[svb]

Yesterday I took her out for a shopping tour to Palm Springs, LA and back to San Diego. Obviously it was hot as heck out near the desert but thankfully my AC was cooling effectively. However with the AC on she wants to stall when I go into neutral and but then she fires right up again. I never have this problem with the AC off, never once. Is the compressor pushing the revs down to far? Is this correctable?

[janz]

Wow you take that car off the pavement? Anyways what is the rpm set at when AC is not on? Yes the AC compressor will knock the rpms down sometimes as much as 200 rpm. I had mine set at 880 Rpms with no AC but with the AC on I experienced the same as you. I upped my rpms to 1000 with no AC on and it made a big difference when running the AC it would only drop to 900. As far as I can tell the DME and fuel injection system cannot sense when there is a load at low rpms and then correct for it on our model year cars.

[Brad394]

I have an '86 and have no problem with rpm drop. What it does do is dip about 200 but then settles back at normal idle.

[JFairman]

Porsche could have eliminated this issue like BMW did before the days of motronic and it's computer controlled idle control valve, but they didn't.

I eliminated that problem by installing a bosch 10mm ID vacuum solenoid that can be intalled as a throttle body bypass. I pulled a few of them off big 6 cylinder BMW's with L-jetronic injection at junkyards.
I don't have the part number on hand right now but all the 6 cylinder BMW's with L-jetronic in the late 70's and very early 80's had them, and they are mounted right next to the throttle body and used to keep the idle from dropping when the AC compressor is switched on.

On any engine, just wire it up to the same wire that turns ion the AC clutch. T in somewhere before and after the throttle body with 3/8" fuel line and when installed it will open when the compressor comes on and let air bypass the throttle body keeping the idle from dropping.
By itself it will raise the idle 300rpms and if the AC is charged correctly thats about the correct compensation.
I also put a small brass air tool ball valve in the 3/8" bypass hose to adjust air flow perfectly so the idle speed would be exactly the same when the AC compressor comes on.

I T'd into the hoses on each side of the auxillary air slide valve that raises the idle speed on CIS cars when cold. I also drilled out the inside of the T's and the ball valve to as close to 3/8" as possible to let as much air through as the solenoid. took some time but was worth it and it works perfectly. You have to dismantle the ball valve and clean the burrs and metal dust out after doing that.

Here's pics of the bosch vacuum solenoid and small air tool ball valve I modified to control the idle speed when the AC compressor comes on. This solenoid bracket might have come out of a vlovo or mercedes, I can't rememeber. I found unused mounting bosses, one with a stud in it already on the botom half of the CIS housing that lined up perfect and I mounted it there.
This is on an '87 930, and the intercooler was off the car when these pics were taken.

[DRACO A5OG]

I found that if I lean her out on the AFM, the A/C wil have no effect on my idle. when rich, It will sub dip then stall at stop. I use to push the clutch in to prevent the stalling before I adjusted the A/F ratio to leaner settings.

My observation.

[glennspiegler]

I have the same problem. Could Draco explain the AFM and how to do it. Have read about checking the CO but I dont have a tester and they say to connect it to the cat which is gone on my B&B. Next the Workshop Manual discusses bridging the test jack in the engine compartment to disable the idle volumetric control and then adjusting the idle by turning the screw on the throttle housing to adjust the idle. Could I just make this adjustment to increase the idle 200 rpm to prevent the stall without checking the CO first. Thanks