where's your Idle at ? 850, 900,950,1000, 1100 RPM's

[heliolps2]

I have found that my car seems happiest between 1000 and 1100 rpm's I have a 930/66 motor , well maybe not anymore with all the mods I have done, including 964 cams . the manual says 1000 +-50 rpm's,

Right now it's set at 1000 rpms and the afr is @ 14.0 -13.9
but if i bring the rpm's up to 1100 the afr's drop to 13.6-13.5 , I can fine tune the afr's with idle screw,has any one else expeinced this ? not that I think it's a problem,

I just wanted to see what other people are doing out there.

[JFairman]

800 or the first hash mark below 1000 whatever that is.

[oilonly]

Just under 1000 with an AFR of just under 14.

[mark houghton]

950 idle rpm, AFR around 13.8

[Ronnie's.930]

Mine is at 1000-1100 . . . this seems to be the sweetspot for my car as well . . . also helps for using the air conditioning as there is nothing in place to raise the idle when the compressor is on (and the compressor is on frequently as I live in TX and like to have the cabin as frosty as possible most of the time)! If you ever hear that TX is "dry heat" the speaker is full of **** - it's a ****ing combinaton of blast furnace and tropical jungle here most of the year. How it can always be 80% plus humidity when it seldom rains is beyond me.

[JFairman]

You can put in a vacuum solenoid that bypasses air around the throttle body butterfly energized by the same 12 volt supply wire that engages the AC compressor from an L-jetronic big six BMW made from '75- '83.
Do that correctly and the idle remains exactly the same when the comressor kicks on or off.

You can get the vacuum solenoids from you pull it junkyards with old 528i - 735i pre 1984 BMW's for next to nothing.

[Ronnie's.930]

I am going to do that soon (learned about that from you in that other " B&B intercooler" thread) - thanks!

[heliolps2]

Hello JFairman , 800 seems low? what cams do you have ? and what ignition ? do you think even matters what you have ? My car isn't very happy that low,

Maybe next time I adjust my CO, I will set it with the rpm's at 900-950 see if she likes it, what most be happening is when I turn down the Idle the afr's goes way lean then she's not happy,

Is there any benefits having the idle on the lower or higher side ?

[JFairman]

I like it at 800 rpms and it's perfectly smooth and happy there.
964 cams, around 13.5:1 idle AFR, MSD 6al ignition and blaster high vibration coil, Napa solid brass conductor rotor with no resistor, magnacore wires and Bosch W4CS plugs gapped at .040"
Steady cruise AFR is around 15:1 and full boost AFR is around 12:1 at 6000+ rpms.

I have the CIS flowtech 20% over modified aluminum fuel head and Brian Leask adjustable WUR with summit racing digital rpm switch and vacuum solenoid tuned about good as possible I think. it starts and runs absolutley smooth and perfect all the time.

Some people still mention 14.7:1 as the correct idle AFR. It was back when gas was gas but not anymore when ethanol alcohol is mixed in with it.
The alcohol molecule has oxygen in it so that affects the AFR leaning it out a little.
Todays common pump gas with 10% ethanol which can also be called E10 gas has a Stoichiometric Air-fuel Ratio of around 14:1 - 14.2:1 and you can run 15:1 to 15.2:1 steady cruise AFR with no problems and get a little better gas mileage.

CIS fuel pressure at the injectors is down around 40-45 psi or just above cracking open pressure at idle speed and they're spraying continuously while the intake valve is closed so they do not atomize fuel as well as when you speed up the motor and injector pressure goes up injecting more fuel. Thats probably why a CIS 930 motor idles smoother between 13.2:1 and 13.8:1 AFR.

[heliolps2]

JFairman thanks for chiming in, Great set up, you seem to have it tailed in. I have a similar set up , 964 cams , Permatune with no coil, Carrera cap ,rotor & wires,timing at 29 degs , W4CS plugs gaped at 0.30, I have stock (at least I think its stock) euro blk fuel head that flows 320 mil per min , euro line and 009 injectors

I live the DC area so weather is not as nice as FL , saying that it's harder to get a grip on a good setting for year round driving , I have to change my setup for colder and for warmer months, for cooler months I have it at the 14 to 13.9 Idle and @ cruze 14.7 on warmer month 13.5-13.6 Idle and cruze the same ,

I can bump up my system pressure 6.9 to 7.2 then I can get 15.1 to 15.3 on cruze ,I'll have to see if it changes my on boost afr's also, Do you think it's safe to run in the low 15's on cruze , we also have the E10 gas here , 93 octain

I have a hand held Innovate wide band that I can switch to 14.1 stonch for the E10 gas, then I get all confused how to set up the can using those numbers , I just leave on the 14.7 stonch settings.

Please shed some light on this for me please, thanks

[mppickett]

Similar motor specs to you except Carrera 3.2 intake, EFI & EDIS. It likes to idle at 1000 rpm & 13.8 AFR.

[mooney265]

800 rpm... Much quieter

[heliolps2]

mppickett you have message

[MikeD930]

Mine is set around 900 rpm. Used to be around 700 rpm...it would sometimes hunt for idle under certain conditions so I decided to bump up the idle to 900 rpm. It helped minimize hunting for idle. This car is with Protomotive EFI system.

[1986 930]

Mine is at around 900 when it is not hunting for the idle. I have it in the shop for a new O2 sensor, amongst other fixes, in the hopes that that will finish my CIS Restoration project.

[heliolps2]

I love my CIS, It seems 900 rpm's is the number most people or going with, Hmmm

[wjfk32]

1st mark below 1000.


Walt