CIS - Warm idle problem on SC with 964 cams

[P0rsche]

Hi,

First a photo of my car which is a 1981 SC ROW



The problem exists since I rebuilt the motor and fitted 964 cams. I never adjusted the mixture before I did the rebuild so am not sure if it was somehow adjusted to compensate for the problem or if it is a new problem.

When I did the rebuild I replaced the following on the intake system to prevent leakage:
O ring under throttle body
O ring under fuel distributor
Gasket under air flow sensor
6x rubber couplings on intake runners
O rings on injectors
O rings on injector fittings in intake runners
O rings on cold start injector

I have sprayed plenty brake cleaner looking for air leaks and found none

My air box appears to be in good condition and I have fitted a pop off valve
Cold fuel pressure at 10 degrees C = 1.6 Bar
Hot fuel pressure = 3.7 Bar
System pressure = 4.7 Bar
Residual pressure in spec
Injector spray pattern good
Injector leakage test ok
Fuel volume sprayed from each injector is equal - tested at partial and full air sensor flap opening
Auxiliary air valve tested ok

Mixture set when hot so idle decreases if I raise or lower the air sensor flap slightly (This is how I have been told to set it). I tried setting it with an electronic tester using a lambda sensor but if I set the air fuel ratio to 14.7:1 (which I believe is correct) then the idle is rough so I set it the manual method as mentioned above and noticed the air fuel ratio was about 13.5:1. I don't know if a lambda sensor can be faulty or if
14.7:1 is incorrect.
Idle speed when hot = 1000 rpm (I know it's a bit high)

Engine starts easily when cold and hunts for a few seconds then idles at 800 rpm Engine continues to run and idle fine for the first 4 - 5 minutes For the next 7 - 10 minutes the engine continues to idle at 800 rpm but if I press and then release the accelerator the car cuts out (it appears to be running rich) so every stop I make the engine cuts out.
When the engine starts to get hot it does not quite cut out, the rpm drops to about 200 and then hunts up to 1600 and then stabilizes after a few times or still cuts out When the engine is nice and hot it idles fine at 1000 rpm. If I rev the engine and then leave the gas it does tend to dip down to about 800 and then recover to 1000

If I turn the mixture screw out (leaner) by about 1/4 turn it seems to improve the warm idle problem but then idles badly when hot

Hope you can help!!
Chris

[john walker's workshop]

find a shop with a gas analyzer and set the CO to 3% to 3.5% with the O2 sensopr unplugged. then leave it unplugged.

[P0rsche]

Thanks John, I'll try that as soon as I have the torsion bars back in.

Something I forgot to mention, there is none of that emission control stuff on my car that some of you guys have.

[john walker's workshop]

ignition timing at about 33° total advance gives a stronger idle too. less tendency to die with a little more initial advance.

[Gunter]

Chris:
What cam timing did you use for the 964's? Mine are set at 1.4mm.
What ignition timing?
Did you service/lube the distributor? Is the vac advance working?
I posted an easy way to do clean/lube and like JW says, set it to 33 deg total advance.
With the hunting you describe, I suspect a mixture problem.
I set mine by ear, adjustments between the mix screw and the fast idle screw.