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350matt
350matt, Engineer - BEng Hons
Category: Saab
Satisfied Customers: 20577
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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I have a 2006 Saab 9-2x. I get a weird rpm surging issue.

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I have a 2006 Saab 9-2x. I get a weird rpm surging issue. Everytime when it is cool outside and the car is started high idle engages ~1200rpm but when put in reverse and rolling down the driveway clutch in it revs to almost 4000 rpm. Same happens if you depress the clutch in any forward gear when cold. Normal operation returns during warmup. When op temp reached especially when hot behavior returns although more rev holding or slight surge 2000 rpm-2500 rpm when clutch depressed. I've had both the ecu update from Subaru which had a tsb for a similar issue as well as the throttle body replaced. Still no luck. It's driving me crazy and scaring the neighbors children when I leave the house for fear of me trying to run them over. Thoughts?
Customer: replied 1 month ago.
I should add that during any of these rpm surge events it is when the 5sp manual is in gear,clutch pedal depressed, foot completely off the gas and the car is rolling/coasting. By moving only the shifter into neutral clutch still depressed revs quickly drop to either high idle or normal idle depending engine temp. What I mean by warmup is when the engine temp gauge moves off cold and has not yet reach normal operating temp

Hello

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading

Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

Customer: replied 1 month ago.
Ok great. I will try the above i assume by air flow meter your referring to the maf sensor on this car. Also the car had been at both a Subaru dealer and a private garage I use no luck unfornately although they did due a throttle body flush. Anyhow I will start the above troubleshooting procedures and see how it goes

Hello

thats correct airflow meter = MAF ( mass airflow sensor)

just get back to me on this post

Hi

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Customer: replied 14 days ago.
Hello Matt,Sorry for the delay I haven't had a chance to take a look at this yet but once I do if I need further info I'll be sure to reengage.Cheers,Ryer

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