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Saab 9000, 1996 causing a bit of a problem. On start-up, idle can be erratic and engine sounds as if its missing badly. Most times it settles down to normal idling and engine note improves. However, it can also happen when driving causing fuel consumption to increase dramatically and a loss of power. Is this a ECU problem or am I missing something? Car has 130K so don't want an expensive fix. Ideas please?
 

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Hi Peterstam,

Usually ECUs are not a problem, more likely one of the sensors that send info to the ECU. From what you say it sounds like the miss fire is due to an over rich mixture or no spark.

Like Saabchick says check those plugs first - are the NGK of the right spec and gap, what do the electrodes look like.
Next off, is to check electrical connections - pull apart clean and reconnect. Also check all the vaccuum pipes and the one-way valve between the rocker cover and the minlet manifold.
I assume the check engine light isnt coming on when the miss fire occurs? Is the cooling water and oil OK, no signs of the two mixing or lose of water?
Could be the DI rail but I think these tend to cause miss fires under high load rather than at idle. They are £150ish new so best to 'borrow' a known good one to try.
What model of 9000 have you - if its a turbo also worth checking the recirculation valve.

Have fun and let us know how you get on.
 

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As Saabchick says - could be DI pack if fitted or are you on a distributor?(rotor arm, cap or leads dodgy) Is it just one cylinder or all of them? Does it do it everytime or just occasionally and have you checked plugs to see if they look sooted up? or is your exhast smoky(black rather than blue)- does it do it under load or all the time?
The ECU's are I believe quite reliable, at least I have not heard them mentioned as a regular item to replace.
 
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