C900 occasional stalling on approach to junctions

[James]

As the title says ... 1994 C900, runs beautifully, but sometimes stalls when changing from 3rd down to 2nd.  Usually just after the car has warmed itself up properly.

Should I start by replacing the vacuum lines?  Or should I be tweaking the idle (which does appear a bit low).

[Saabman]

For the sake of a small amount of money I'd swop the vac hoses anyway, there's a good chance they will be brittle anyway plus it gives you a chance to route about and possibly spot other problems.

[phoenix]

Sticky idle control valve is a possibility, but it is also a symptom of a failing AMM. Is yours Lucas?

[ianrobbo]

If it's Lucas, it needs an incoming speed signal - mine used to stall a lot, I was convinced I had some kind of vac problem, but once I replaced the speedo cable that had recently broken, hey presto, all was well!

So, before you go changing your vac hoses, idle air control valve, AMM etc etc, does your speedo work?

Failing that, I too would start by replacing the vac hoses.

[AdamH]

My lpt automatic used to stall at junctions regularly. I tried cleaning the idle control valve, but never had any joy. As an auto, restarting was a complete pain.

[ptanser]

Also clean the AMM, if that starts playing up that can cause stalling

if you need to replace it don't buy a Saab one as they are expensive (even used ones)

look the lucas part number and you can find the same AMM used on other vehicles (I think Some Jag ones are the same ) but cheaper the just change the housing

[James]

Thanks for all this folks -really helpful, and exactly what STT is for I'm back home tomorrow after a couple of weeks away, so I'll get to it and let you know how I get on.

[James]

Right, large roll of red silicone hose arrived yesterday, so I've spent this morning cursing and swearing.  Some of them are a complete pain in the **** to reach.

I'll take the car out for a spin later and report back

[James]

So the idle's not perfect but it's a lot better, and the stalling appears no more.  It still dips more than I'd like when (eg) pressing the clutch pedal after rolling along at zero throttle / overrun in 4th.  But I can no longer make it stall on demand by dipping the clutch after accelerating on boost in 3rd, which would always do it before.

This is after replacing as much of the vac hose as I could reach without removing too many other bits.  Next step is cleaning the AMM and whatever else needs cleaning, but that'll have to wait a while.

Thanks all

[supremedalek]

A can of carb cleaner spray over the air passages/vacuum lines while engine is idling (i.e. vaccum) can help you find out other possible leaks. Remember, if you spray somewhere and idle goes up, you found a leak.

[James]

Thanks - much carb cleaner expended and it's very nearly as it should be.  My Saab tech reckons next step is to replace the AIC but I'll wait and see how it goes. I think the cooler weather is helping too.