Erratic idle problem
 

Hi guys,

This problem has been driving me mad for a while and I'm really struggling to get to the bottom of it. The car is a Forester XT 2.0l turbo and the issue is as follows:

• When sterted after sat for 12 hours or so and completely cold it'll run very rough for the first 10 seconds or so.
  
• While the engine is below normal opperating temp it'll rev itself while the clutch is depressed. For example when pulling up to a junction or into a parking space as the clutch is depressed it'll rev to 2200 or so several times.
  
• When warmed up it will still idle unevenly, sometimes at about 1100 and sometimes at 600 or so where it idles quite rough.
  
• When Changing gears, especially in the higher rev range, as the clutch is pressed the revs will hold or even rise by 200 or so before slowly dropping down.

What I've tried so far:

• New MAF sensor - no difference
  
• New front O2 sensor - no difference
  
• Tried a different Idle Air Control Valve - no difference
  
• Looked at the TPS read out (via SSM / OBD2) and it's reading 0% untouched and 100% foot to the floor so I assume I can rule this out.

Looking for suggestions of what else it could be, anyone had a similar problem? I'm a bit lost really, thinking it could be a vacuum leak but not shour of the best way to diagnose and find this....

Any help would be greatfully appreciated!
Thanks
Tom

Any codes stored at all?

Was the new MAF new, or just another one? Was it of the correct type for your vehicle?

If the answer to these is no, yes, yes, get it to a specialist.

Melton Mowbray is near you, Carnetix are highly recommended.

The MAF was a new denso with matching part no.s to the old one.

I'm tring to avoid taking it to a specialist, I don't really have the money

Try checking for vacuum leaks around the inlet manifold, could be a split hose or one may have popped off

What's the best way to check for leaks, I've has a visual look but it's a pretty complex system, any known weak points?

Spray some carb cleaner around the inlet/pipes etc... listen for the revs to increase. That is how i find leaks. I would also replace the coolant temp sensor, the one for the ecu not the dial.

Woops...shouldn't have bought a Scoob then:(

Sorry but older Subrau Impreza = moneypit.

ok great I'll give this a go, thanks!

could just be the idle valve.

Ive tried replacing the idle valve but the problem still continued so I'm guess it's not the problem...

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