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Discussion Starter #1
Hi - before I get going on this one, many thanks to all who helped in the search for my extremely elusive APC ECU earlier this week... got the boost problem sorted in the end - turned out to be a bad earth on the APC valve. Now my baby really shifts... :cheesy: :cheesy: :cheesy:

Now that's sorted, I'm on to the next item on my (long) list - occasionally when I brake sharply, the engine stalls, usually at the worst possible moment. It happened today on a busy roundabout - not funny:( .

I'm thinking it's one of two things: either the auto box isn't 'disengaging' quickly enough when I slam on the anchors, or the idle control system isn't taking over from the main system smoothly...

Any thoughts/ideas would be greatly appreciated...
 

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Probably the turbo bypass valve leaking.

Fred's idling guide said:
On a Turbo the Dump or Bypass Valve (Classic symptom "When I come to a quick stop, usually in traffic or when someone cuts me off or at a red light, the idle drops from just under 1000 to almost zero and the car stalls.") The diaphragm in these plastic valves fails and leaks vacuum. If you can suck air through the small-bore pipe to the valve (which is down front of engine above turbo) it's broken; they are reasonably cheap (£20) and quick to replace. Sometimes failed hose clamps on these valves cause the same stalling problem.
http://www.saabcentral.com/techhelp/c900/idling_problems.php .
 

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When you brake to a halt or just slow down?

One thing that occurs when you brake sharply is that the brake servo dumps vacuum. It might be that you have a vacuum leak already and the brake servo dumping is exacerbating the problem.

You could also check your throttle dashpot whose job it is to keep the throttle from closing too sharply. Also consider is your turbo bypass valve working properly. Dunno if that would cause an engine stall though...

Jezzadee said:
Probably the turbo bypass valve leaking
Ok, now I know...
 

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Discussion Starter #4
Jez, I think you may have nailed it - I can both suck and blow quite freely through the vacuum pipe to the dump valve... it may also explain why the idling is a little erratic as well.

Best get one of those ordered, along with some nice clear indicator/repeater lenses to smarten things up a bit at the front...:cheesy:

Thanks!
 

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Sorry if this is really dumb, but after reading these idling/stalling threads I want to get a new bypass / dump valve too. But what exactly are they called and where from? The two obvious uk saab parts sites don't seem to offer a bypass valve for £20. And should I be searching for a bypass valve, or a dump valve, or a turbo bypass valve. Me Haynes offers no advice on the matter...:)
 

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I got a replacemend turbo bypass valve from my local Saab dealer for about EUR20 or so. PFS have 'dump valves' but they start around STG99
 

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cdaly said:
I got a replacemend turbo bypass valve from my local Saab dealer for about EUR20 or so. PFS have 'dump valves' but they start around STG99
Cheers cdaly, I'll try that, I have one close. Is it a straightforward job to swap, any adjustment needed? I really must buy a Bentley manual...
 

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Jezzadee said:
There's a guide here , although it seems to have lost the pics.
Cheers J, v helpful. The 'Silicon vacuum line' it mentions, is the done thing just to buy a long length and cut to size as needed? I see from another article you linked to when I was researching this :cool: stressed it was important to check these too.
 
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