930 Idle speed rpm.
 

Hi, I have a 1984 930 and want to know the correct idle speed rpm with OEM air conditioning "optional equipment". The Porsche Workshop Manual say idle speed rpm for 930 (all) is 1000 +/- 50. I want to know if this specification change with the air conditioning system, because when the idle speed is set in 1000 rpm with AC (OFF) and then you turn ON the AC, the rpm drop to about 800, and I really don't know if 800 is to low for 930 considering the OEM specification (Porsche Workshop Manual) 1000 +/- 50. I 'll appreciate your comments, thanks in advance!
Best,
Leandro

I have a 1982 930 with factory air and that is about what my idle speed. I might be slightly lower, 900 rpm AC (off), 800 AC (on).

Thank you so much Capt Bob!
I appreciate your info; have a good afternoon my friend...
Best,
Leandro

I wouldn't worry about it. If it keeps you awake at night, then turn up the idle speed to 1100 without the A/C.

My A/C no workie, and I run my idle at 950 to 1000.

nice to have same question in 2 forums.

see my answer on the 911 side

Hey Mark H., thank you for your comment, yes keeps me awake at night!!! My idle speed now is 1100 without the A/C. I 'll check it a few days and maybe go down to 1000-1050 to match the Porsche Workshop Manual.
Also thank you T77911S for your info, yes sorry about that, I asked in the 911 side first because the title of this forum say "Technical Forum" and later found the 930 side; but always is good idea meet new friends with the same classic Porsche pasion!
I really appreciate your help...
Best,
Leandro

After doing a search I decided to pile on here and not start a new thread. Since the temps have cooled of here finally, I am driving the 930 a lot more. During the past several drives, the idle speed is now at around 500 rpm (no ac). From a standstill (red light) if the car is idling at 500 rpm, pulling away with a tip in of the of the throttle there is slight miss/backfire, then once beyond that it drives fine. at a standstill, I can rev it 900 or so rpm, and it will hold steady if I keep it there. Also at WOT/full boost, when I back off or hit the rev limiter, while is sounds cool, i'm getting more shot gun/cannon blasts. Maybe it is just because I have not driven it much and getting back used to the sound? I did go back to a single out pipe on the left side, where before I had the dual out / one on each side. Should I just turn up the idle speed and see how she runs and go from there?

500 is way to low,

These cars don't have a mechanism (like modern cars) to increase RPM when you hit the AC switch - so the extra load brings idle speed down a little. C'est la vie.

I suggest you check timing and fuel mix and see if that brings your idle speed back up to 950 or 975rpm (assuming you need to adjust them). If no adjustments needed to either then I recommend adjusting idle to 950 or so rpm. 500 is too low. stumble off idle sounds like timing issue or fueling issue. backfire on decel could be unrelated but could be either, as well. But i would not worry too much about the decel and focus on the accel and idle first.

Correct, but it's real easy to install one.
Go to a salvage yard and yank one off an old BMW or Mercedes that has one plumbed to the plenum chamber next to the throttle body and wire it to the 12 volt wire that engages the AC clutch.
You can also install a tiny ball valve to adjust the AC on idle speed exactly where you want it.
Then there is no change in idle speed when the AC compressor engages.

I have a 81 with the a/c disconnected. I like to be at 850.
And yah, I agree 500 is way low. I’d think you’d have oil starvation with extended idle but honestly that’s just a guess. But it sure would be a shame with that beautiful beast of a motor.
Chris, is there a reason you’re running so low ?

500rpm idle speed is too low.
There's a chance oil pressure and flow would be so low that the cam spray bars in the cam towers would not spray enough oil on the cam lobes and rocker arms to lube and cool them. Then they would self destruct and make an unbelievable mess of everything in the motor, the external thermostat, oil lines to the front oil cooler, and both oil coolers... the one on the engine if it's still there and the one in front of the right front wheel.

When I had a 1987 911 turbo with AC I had the idle speed set at what looked like 800 rpm on the tachometer. I liked the sound of the motor there and everything worked great.

Thanks for the advise. I have been keeping the revs around 900 or so while stopped to not starve for oil. i'm sure I can find it but any suggestions on about where the timing should be set at?

To the OP, I don’t mean to highjack your thread but I think that jfairman’s post neads further clarification.
.....yank what off an old BMW or Mercedes? Also instal tiny ball valve?
Please expand, thanks.
Johan

cellison, I think the spec says 950 or 975rpm is the desired idle speed when fully warmed up.

Sorry I didn't go into more detail before.

Older Bosch EFI motors like L jetronic and K jetronic had a Pierburg idle control valve that opened and bypassed enough air around the throttle body to raise idle speed around 200 rpms if no extra load was put on the motor. It was supplied 12 volts at the same time the AC pump clutch engaged so idle speed would remain the same or real close to it when the AC pump was engaged.
It was either open or closed all the way with no steps in between.

When Motronic EFI came around the idle control valve was changed and improved so it could open varying amounts depending on load, altitude, or whatever so it would control and maintain the idle speed at the factory set rpm at all times if everything was working correctly.

Thanks s5uewf. I was idling around 950 before. I was wondering about where the timing should be set at when idling at 950 rpm. I have seen differing information.

Different years may be different as far as ignition timing specs. The factory had to retard the ignition timing to the point is was after top dead center to raise exhaust temperatures in catalytic converter equipped cars so emissions would be low enough for the cars to be sold in some countries like the USA.

That makes answering your question difficult. The ignition distributor in your car may have been modified by a previous owner or it may not be working correctly anymore. You obviously don't know because you're asking this question.
Therefore for the health of your motor it's probably best to leave it alone unless you have knowledge from experience and not from reading forums.

When I had an '87 turbo the stock ignition timing was so retarded when I got it you could get out and run faster than the car could leave from a stop.
I don't remember the factory ignition timing specs but they were on a grey sticker on the bottom edge of the engine lid.
I had ignition timing at idle speed around 10 degrees before top dead center and I had the two centrifical advance weight stops down in the bottom of the distributor bent inwards a little so maximum advance was reduced to around 30-35 degrees before top dead center while idle timing was advanced that much. You have to do that when advancing idle timing 10 to 15 degrees or else maximum advance will be too much and that will cause detonation or even worse preignition and that will break piston rings or destroy the motor.

Maybe you should get in touch with Turbokraft and ask them what you can do.

Thanks for the advice. I have "heard about 5-15 before TDC. The distributor was not modified by the PO and everything was set about 1k mile ago by the shop who did all the work. I'll contact him as he knows 930s and his mods/set up similar to mine. I just wanted to get the light out and confirm / reset if needed before going further.