Only recently when i'm driving my 86 944 in the extreme cold does it have a problem with idle. Once the car has warmed up the idle will drop from normal range (800 rpm) all the way down to the first or second hash mark on the tach (200rpm?) but it won't die, it will just sputter away there. Once gas is given, the engine perks to life as if nothings wrong. This only seems to happen when temps are around 0 degrees or below (F) and only once the engine has warmed up. Any ideas?
Not to the extreme that you get, but similar happens in my Saab. Does the 944 have an AIC (Air Idle Control) valve or something similar. I believe there is one on a 911 engine of various type. It is part of Bosch LH type injection system at least.
It's there to control intake/fueling at lower temps (like a cold idle circuit). They have a large air pipe attached to the body (actually two in a loop from infront to behind the throttle plate on the throttle body and an electrical connection. Inside the AIC is an electric controlled sliding flap/plate. That can get gummed up and either stick open or closed. Depending on where it sticks you either get a racing idle or in your case a low eratic one. Sometimes if it is only partially gummed, it will move but slowly instead of snapping back and forward and means you can experience a little of both.
Once removed/disconnected from the car, you can usually clean it with spray carb cleaner, or even WD40(or similar) spray freeing oil/water displacer and a toothbrush. Should help some if such a device is fitted.
Of course sometimes they just wear internally and it leading to leaks etc, in which case, replacement is the only option.
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