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I have an intersting issue. When the engine is cold, and I start the vehicle the cold start fires up and hold idle at about 100rpm. Very shortly after as the car is coming up to temp the idle falls off to about 400rpm. This seems to be a product of the cold start system. Where should I look to keep the RPMs up until the car is fully warmed up?

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is it an 8v 0r 16v

if its an 8v it could be the cold start sensor is past its best,eg cutting out to early giving rough idle?:roll:
 

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So the idle drops when the engine starts to reach operating temperature - that'll be when the AIC is closing then. I suspect that the problem is with the idle adjustment screw on the throttle body - thatmight not be letting in enough air to keep the idle high, once the AIC closes.

The idle adjustment screw regulates airflow through a bypass channel on top of the throttle body.

The adjust screw is in the centre of this picture:


I would clean out the pre-throttle body intake piping, using carb cleaner and a rag. Then clean out the throttle body itself. You could remove the adjustment screw completely and flush carb cleaner through the air channel, incase that's gunked up.

You can find some other ideas here:
http://www.saabcentral.com/forums/showthread.php?t=34997
http://www.saabcentral.com/techhelp/c900/throttle_valve.php
http://www.saabcentral.com/techhelp/c900/idling_problems.php

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We still need to know if this is an 8V or a 16V.

Matthew - is your picture a 16V throttle? My T8 does not have that adjusting screw. I have a throttle stop screw (the smaller grub screw), but the AAV is adjusted on the valve itself, rather than at the throttle.

My experience of 8V cars dropping idle is when the AAV is not working properly. Usually, a simple blow through with carb cleaner is enough. Otherwise, I'd be looking at the thermo time switch.
 

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Matthew said:
The picture is of a 16v throttle body. I hadn't thought that 8v cars might not have an idle adjustment screw.
I've owned a 1988, 1985 and now, 1989 MY 8V and don't recall that screw on any. Given your more extensive knowledge of C900s than mine, I'd bow to your better judgement ...

The 8V cars do have an idle adjustment screw, but it is done at the throttle stop ... on the ones I've owned, anyway. That is not to say that all 8V SAABs are the same. I think we need to find another solution here, if it is an 8V car we're dealing with.
 

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Re cold start issues:

I have a 900i 8 valve. 1989 model. when starting the car in the morning recently, it seems like the car is choking / spluttering, it does not cut out but the revs drop to 500 rpm typically..so I give it a bit of gas and once the car is warmed up.. the lumpiness settles down and the idle speed is fine. (The cold start injector is disconnected..as its faulty, (it was floading the car)..and the car doesn't seem to need it).

I have checked the Auxilliary Air Valve by disconnecting both pipes and it seems to be working fine..as the car is left to sit for 2hrs + it opens up and is fully closed to a tiny slit after a few minutes.

Can you diagnose my problem please? I'm now thinking Thermo Time Switch / Warm Up regulator??? (The air filter was changed 15k miles ago..so I think that needs doing also) what action to take?
 

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I have a 900s 8v (1987) that does the same thing on startup. Sputters for like 30 seconds and the everythign is fine after that.


Steve
 

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Just on a side note, I have an 8v and the idler adjust screw is identical to the one in the pic :)
 
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