944 Cold start issue

[Porsche944Owner]

Hello,
I'm having a problem with my 1983 944 having trouble starting cold and idling rough until the car warms up. I did some research and came to the conclusion of the Auxiliary Air Valve, as the car runs perfect after warming up, and starts great too. I'm at the point of testing the AAR, putting in the freezer to watch it open, letting it sit in room temp to let it close, and hooking it up to electrical leads to let it close more.
So does this mean the AAR is not the problem?
How much should it be opening as that should've been the problem?
Where to go from here? Order a rebuilt one from 944online?
Thanks for any help

[walfreyydo]

Change out the DME temp sensor (blue top) cheap and easy and critical for the DME to know when to richen or lean the mixture for a cold/hot starts. Another potential issue is a vacuum leak (unmetered air), or your TPS isnt working properly and its not telling the DME you are in an idle state.

More info and testing information here:
https://www.clarks-garage.com/shop-manual/ts-01.htm

ICV/AAR is more related to erratic idle issues, and one way to test it is to hook up 12V and make sure its opening and closing without impediment (it should cleanly snap open and closed). Usually these fail because they get full of gunk which restricts their operation, and can be sometimes cleaned with carb cleaner. I am not sure why you would put it in a freezer as it is not controlled by temperature, so thats confusing as to where you got that from. Regardless, I recommend your DME temp sensor gets replaced (they are like $15) and if that doesnt resolve it, look for vacuum leaks/smoke test and test your TPS.

[Porsche944Owner]

I have changed out the DME temp sensor, and as far as I can tell, the vacuum lines look great, but I will test this more. I should have mentioned along with the hard start, the car idles erratically and will sometimes stall until warm. When I replaced the DME temp sensor this did improve, however the issue persisted.
If not controlled by temp, what is the AAR controlled by? I was under the impression the AAR slowly closes as the car warms up due to the mechanism inside expanding, and therefore would open when the car is cold, with the freezer simulating a cold day. I understand this is quite abit different the ICV of the later cars. Like you said, I suppose I will shift my attention to the TPS.

[walfreyydo]

Surging idle is typical of a lean condition. That can be cause by some sort of vacuum leak of unmetered air entering the system, or incorrect air metering (AFM issue, see clarks walkthrough on testing and moving the contact points) or wrong DME fuel map (TPS) or a mixture too lean for cold startup (DME temp sensor issue). A rough, non-surging idle could be caused by a rich condition as well, too much fuel, for instance, if the TPS isnt registering the idle state, the DME could be using the part throttle or WOT maps, causing it to be very rich. I suspect you have a small vacuum leak, which can be identified through a smoke test, or other means (youtube is a great resource and diagnosis techniques need not be specific to a 944)

These cars have two temp sensors, the blue top sensor is the DME temp sensor and the second temp sensor tucked under the intake is the gauge sensor.

[originalowner]

Originally Posted by Porsche944Owner

what is the AAR controlled by? I was under the impression the AAR slowly closes as the car warms up due to the mechanism inside expanding, and therefore would open when the car is cold, with the freezer simulating a cold day. I understand this is quite abit different the ICV of the later cars.

This is the correct behavior for an early 944. The AAR has a coil of bi-metallic strip connected to a butterfly valve, and a heater. Cold it starts out open. Power to the fuel pump also powers the AAV heater, which causes the bi-metallic coil to slowly close off the airflow. It takes a few minutes to close completely on a very cold day.

The AAV is on page 1 of the schematic, where it is called the Supplementary Air Valve. There is also another supplementary air valve if you have air conditioning, which is electric binary and opens when the compressor clutch is active.

[walfreyydo]

Originally Posted by originalowner

This is the correct behavior for an early 944. The AAR has a coil of bi-metallic strip connected to a butterfly valve, and a heater. Cold it starts out open. Power to the fuel pump also powers the AAV heater, which causes the bi-metallic coil to slowly close off the airflow. It takes a few minutes to close completely on a very cold day.

The AAV is on page 1 of the schematic, where it is called the Supplementary Air Valve. There is also another supplementary air valve if you have air conditioning, which is electric binary and opens when the compressor clutch is active.

Wow thats really interesting, I guess you learn something new each day. So in a non-AC car it is correlated to the outside ambient air temp and not related to engine coolant temp at all.

[originalowner]

Same for AC cars. The AC car just has an additional throttle air bypass.