Over-revving on startup

[tomart]

Been happening recently - on starting the car ( 2006 9-5 2.3t) from cold in the morning the revs are way higher than normal and don`t drop as quickly as they should. Sorts itself out after driving for a few minutes but revs seem to come down slowly if you pull up, e.g. at a light or a junction. Have had a quick look under the bonnet but nothing obvious like split or loose hoses. No CEL either. Anybody any ideas?

[Finding41]

Is it colder than usual there this winter? It could be adjusting for that cold. Both mine start and run about 1200 rpm for a few min. After they warm up everything is normal.

[tomart]

Is it colder than usual there this winter? It could be adjusting for that cold. Both mine start and run about 1200 rpm for a few min. After they warm up everything is normal.

Not really - it was 8c when I started it up this morning. And the revs are more likely to be at 1500-1600!

[Finding41]

How long since a new air filter? Could it be trying to compensate for something like lack of air? Air fuel mix.

[tomart]

How long since a new air filter? Could it be trying to compensate for something like lack of air? Air fuel mix.

Thanks for the input but car was serviced in December with new oil, air, fuel and cabin filters......

[Kenneth Pain]

Sounds like a loose or leaking vacuum hose.

Check Throttle body (clean if needed)

Check hoses coming off of the Air intake manifold (replace if needed)



Usually I would replace all of the vacuum hoses and check valves that you can visibly see.

Recommendation:

Check hoses that connect to:

Fuel Pressure regulator -

Boost Bypass Solenoid -

Plastic hoses that connect on intake (nipple seal might be dried out)



Last but not least -

You may need to reset the throttle body - (re-calibration)

There is a tech guide on how to do it. (Your car does not need to be in Limp mode to be reset. This will allow the car to auto calibrate the idle.)

How to Reset Saab Trionic 7 Throttle Body Limp Home Mode - YouTube

[walawala]

broken check valve?

[Kenneth Pain]

Yes: Check valve - http://www.thesaabsite.com/catimages...?mt=1344129582

Another name for it is: Traction Control Valve ETS return valve Located in upper vacuum hose -

http://www.thesaabsite.com/catimages...?mt=1344129180


Each of these check valves work the same except the Purge Valve.


These all need to be replace to maintain 100% Vacuum


And a leaky vacuum system will cause irregular idling over 1000 RPMs

[tomart]

Have been away so have only just caught up with this thread - thanks for the helpful and detailed suggestions. Hope to tackle this problem at the weekend.Will let you know how I get on.
Thanks again.

[tomart]

Managed to track this down - it was the intake manifold pressure sensor ( the one on the large intake pipe just beyond the dump valve) causing the problem. Took it out and found it covered in oil, for one thing. Also , the o-ring seemed to be slightly damaged which, I think, did`nt create a proper seal, thus causing a tiny air leak.
Put a new o-ring on, cleaned the sensor with contact cleaner - all seems ok.
Thanks for all the many helpful suggestions.