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Discussion Starter · #1 ·
On my way home from work today, my Carly decided to play dipsy-doodle with the revs on idle, taking them from about 2k down to almost zero but then picking up before it had chance to die...


Seemed OK from cold and driving was OK... the odd hesitation but at full bore it was almost normal...

As it happened i was going to change the plugs today anyhow... which i have now done but the symptoms remain.. The old plugs were very sooted so i guess its a fuel/air mixture problem of some sort... But what??

Any ideas guys and gals?
 

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Hi Ed

I had a similar problem with my old 87CDi some yars ago. It turned out to be a fuel pressure problem in the end. I am no expert, people on this board know far more than me, but this info might help you!!!

Regards

green9000
 

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Ed,

Could be various problems, but supplimentary to green9000 suggestion, could also be..:

- Fouled injectors (e.g. also indicated by plugs sooted): A bottle of injector cleaner will solve this - and restor a smoother idle.

- AC system, or power assisting (due to wheel being turned whilst car stationary) cutting in. Both of these latter problems should be compensated by the Idle Control valve. Maybe ICV is due for a clean (as it can clog up with oil from the breather).
 

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Discussion Starter · #6 ·
Just removed IAC and sprayed wd40 in it... Much easier in the older 9000's as its between the throttle manifold and the cam cover just two clips and its off... to say that a lot of [expletive deleted] came out of it was an understatement!!


2 weeks or so ago I had to replace the short piece of tubing from the IAC to the throttle manifold which before repair must have caused most of the rich mixture that caused the sooting on the sparks..

Its better but still not perfect... Revs raging from 600-1200 now.. Will see how it goes tonight..

A couple of quick points... if the power steering or the a/c can affect it... (which isnt the case on this occasion) can a duff battery also affect the idle... i know for a fact mine is on its last legs... But so long as it starts the car in the morning id rather invest the money elsewhere on the car... Also whats the significance of running lean on boost... an how could it happen if the general trend is for one of a rich mixture??
 

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Also whats the significance of running lean on boost... an how could it happen if the general trend is for one of a rich mixture??[/QB][/b]
If the air flow meter is malfunctioning it will 'average', so it will run too rich at idle and too lean under boost.
Too lean a mixture is bad news, combustion will run really hot and burn out pistons and valves. That is why the guys that run high boost also have to up their fuel delivery.
 

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Discussion Starter · #9 ·
A second blast of WD40 and allowing it to sit a while in the IAC seems to have done the trick as far as the erratic idle goes

However, the "normal" idle still seems a bit high (c. 1250rpm) is there some way of manually adjusting the idle speed??
 

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Idle can be set by a Saab technician, plumbing into the ECU.

Alternatively, if your throttle stop screw is holding the throttle off the stop plate, you can wind the screw out a little to drop the revs. This shouldn't upset your throttle position switch (if you have one).. unless you wind screw "in".

Haynes manual describes how to set throttle position switch if this is not detecting the 'throttle closed' position properly, which will also result in high revs, usually with fluctations. You will need an Ohmeter.
 
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