Correct idle speed

[moosthuizen]

My '80 911sc always starts up first time, and goes ok, once warm. While cold it does not react properly to the accelarator pedal, misses and hesitates until warm (only for the first minute or 2 after started, thereafter it's ok).

Once it is started it idles at 600rpm and once hot it goes to 8-900rpm. When hot the prevouis mentioned problem is gone. As i understand it, it should (if cold) idle at 1000+rpm, and when hot go down to 800rpm. Mine does the opposite (begins at 600 and when hot ends at 800). What should I look for? I have new plugs, and leads new vacuum hoses, and the timing is at 5 degrees before tdc. I also believe the idling should be smoother.

It is a Euro model with 150k km on the clock, everything standerd.

Marius
'80 911sc

[Lorenfb]

The cold control pressure (adjusted by the warmup regulator) may have an incorrect
setting, i.e. the control pressure is too high when cold.

[jdowty3]

Could also be your Auxilary Air Regulator is stuck closed. It should open when closed to provide extra air to increase the idle when the motor is cold.

[moosthuizen]

Thanks Loren and Jim. I've only had my Porsche for 3 months now, and still have a lot of learning to do. Would you be so kind as to tell me;

1) How and where to check and perhaps set the cold control pressure?
2) How do I check the Aux Air Regulator, where is it?

Thanks

Marius
'80 911 sc

[Lorenfb]

The control pressure is affected by the warmup regulator (WUR) which can be
adjusted but it's a little difficult. The AAR won't affect your missing, only the cold
idle RPM. The WUR will affect both the mixture (missing) and the cold idle.

The AAR has a hose which goes to the throttle body assembly and an electrical
connection (heater) with connects to the fuel pump relay circuit as does the WUR.