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Discussion Starter #1
Hi all,

I picked up my beautiful Saab 900 Turbo S a couple of weeks ago from a reputable Saab garage with good engineers. Unfortunately over the last week it's been playing up. Luckily it has a 3 month warranty so hoping it will get sorted but wanted some opinions on what it could be.

The car starts and runs fine but intermittently when I get to a junction for example and take my foot off the gas/clutch the revs drop really low at idle and it sometimes stalls . It was particularly bad on the really hot day we had and with the air con it was running terribly at idle in traffic, to the point it would stall if I did not keep my foot on the gas - the revs were just so low at idle when the engine was up to temp it was barely ticking over. Even turning the air con off it could not produce enough revs at idle to tick over.

Checked all vacuum hoses and at the advice of the garage have tweaked the idle screw on the throttle housing 2 x 1/4 turns driving and stopping engine repeatedly with each adjustment to allow ECU to recalibrate to no avail. Just did a 10 minute drive and it stalled 3 times at junctions etc. slowing down. Not ideal. Nor safe really.

Thinking there might be vacuum leak or air/fuel ratio is off because it is particularly worse when the engine is hot.

Also not sure if this is normal but the turbo gauge sits just under the orange region when the engine is off? Should there be any air reading when the engine is off?

Shame as the car has literally just had a complete overhaul and had extensive work done both mechanically and aesthetically.

Any advice greatly appreciated.

Some videos of both revs dropping at idle and turbo gauge.
Stalling:
Turbo:







 

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The standard advice is to tighten all the hose clamps on the turbo piping and make sure the blowoff valve is working and the hoses are tight.
 

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Discussion Starter #7
Going back to Garage on Monday - apparently it could be the idle control valve. Not sure if its Bosch or Lucas but will find out on Monday.
 

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Could also be you've got a vacuum leak through the brake booster. It can be a huge vacuum leak and you won't be able to hear a thing over all the other sounds the engine is making. Easy enough to stopper this vacuum port in the manifold, just beware the brakes will be much less effective when testing it out!
 

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[QUOTE="Jim Mesthene, Adjusting the Throttle Stop screw first is a mistake if it's a Bosch system.
[/QUOTE]
It would be great if someone (Jim) could elaborate. What would be correct order for idle adjustment?
 

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The stop screw on LH is set from the factory and should basically never be adjusted. Improper idle is always the result of something else - a mucked up throttle body, a mixture control problem (vacuum leaks, MAF, etc.), or the idle control valve. I can't even remember a time adjusting the stop screw was the solution. Maybe never.
 

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These cars are very old and most of them have had few owners so I doubt that there is many with untouched throttle stop... I wanted to ask for order of checking tps/idle bypass screw(?)/accelerator cable... and (yes) throttle stop... assuming all other things are right.
 

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For 2.4 LH

Clean throttle housing
Loosen Throttle switch
Back off Throttle stop.
Flip butterfly a few times, it will jam in the venturi/opening.
Adjust throttle stop so it cannot jam.
Adjust throttle switch
Leave them alone in the future.
 
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