Scoobyslammed

Couple of weekends ago... I had me check engine light come on down the motorway... So last week booked it in to go on the computer to see what gives... turned out it was the top oxygen sensor... So all in all its cost me £220.00 quid.
But since this has been replaced on Friday just gone... sometimes when I start it off the key... It's start up fine, but when the idle comes back down to rest... its resting slightley under 800rpm, more near 700 until you blip the throttle then it'll be normal again...
Also, started it this morning... now it was abit frosty... so, started it as usuall... but it was only ticking over at 1300rpm ish... which didn't seem right... normally on a really cold morning from cold it would be 1500-1600rpm...
Now, what do we recon here... MAF???
Its only started since the change of the oxygen sensor, will it take time for it to recognise this change, or now it has been changed, the MAF can't hide its problems now...

SiHethers

Hello again mate!

Two possibilities - 1) they didn't reset the ecu after changing the o2 sensor, in which case the ecu will still be using closed loop fuelling correction that it established with the dodgy sensor, so will likely be overfuelling a bit on idle when it first switches over to closed loop fuelling when your car is warming up first thing in the morning.

2) is that they did reset the ecu and this has unmasked a failing MAF.

No. 2 is more likely given your car is ?MY99, plus your ecu would learn the fuelling for your new sensor pretty quickly. You need to get it looked at on deltadash ideally, by someone who knows what to look for.

Where abouts in the country are you, I may be able to help

Simon

Scoobyslammed

My cars a MY00... I think they cleared the ECU of faults... would that be a reset... I took the car to the main dealer in Newcastle under lyme...
Im in Crewe, cheshire m8ty...
They've told me too take it down again tommorrow, so if I get no joy... I'll get back to you lot... I'm really thinking about just changing the MAF as I've had the car over a year now... and I ain't replaced it yet... but it's only started to idle funny since the change of the oxygen sensor... Cheers for your help... I'll let you know how I get on...

SiHethers

Without looking at the real-time values coming in from the various sensors (MAF, o2 etc) it's difficult to say. Be wary if they turn round and say there's no fault codes stored therefore no problem, because a failing MAF rarely gives a fault code (not before your engines gone pop anyhow).

If they can't find a specific fault just replace the MAF, because if it's still on its original one it'll defo be on the way out by now. The replacement sensors are sturdier as well.

As a precaution I'd avoid driving on boost till you've replaced the MAF. Better safe than sorry (especially as an induction kit will exacerbate a failing MAF due to causing it to misread further)

Hope you get it sorted quickly...

PS if you replace the MAF, only replace the sensor not the full housing (£75 vs £250)

Scoobyslammed

Cheers mate... will do, you don't happen to have the part number do you???

The_Judge

SiHethers

Thank you judge saves me digging around for it.

Keep us posted on the outcome SS

Scoobyslammed

Been back to Subaru today.... they've had it on the computer again... ( for free, didn't pay a penny ), and although the MAF is within there spec... I've decided to changed it, so it will be replaced on thursday along with a reset on the ECU...
We shall see how it goes, fingers crossed that will be it now... The mechanics down there seem dead helpful and very knowledgeable...

bluep

Sounds a bit like the problem i am having with my type r.After a blast down the motorway the check light comes on.All i do is stop,switch it of and on again then it clears.I took the car to the only garage that works at imports here(in n ireland) and who i bought a previous wrx of and they have told me there is three sensors showing faulty and they have said that they will book it in and check them all.I am quite confident and virtually know the car inside out except for the sensors etc.Is there no way i could find out what needs replacing and do it myself as i have access to an excellent salvage yard with all modern cars. car is 97

The_Judge

Indeed there is. Clicky...

bluep

Thank you judge i will give it a whirl on fri when i get home for work and let you know the score cheers again for the guidence.

Scoobyslammed

New MAF fitted + ecu reset... seems bob on now!!! See how it goes though...

Markyboy uk

Be interesting to know how it idles now with the old MAF now that you have had the ECU reset

Mark.

Scoobyslammed

Having owned the car for over a year, it's had a K&n induction kit fitted to it since I don't know when... thought I'd best have it changed, cause they ain't the best induction kits to have on a MY00... Peice of mind now, knowing it has been changed... I ain't got the original airbox to go back on, so I'm probabley gonna go for a induction kit with replacable foam in I think... HKS, or Blitz??? Idle is perfect now, and it's driving A1 now... ain't gonna touch it while its running so good...

The_Judge

Be careful with alternative induction kits. They can screw a MAF very quickly due to vibration. To be honest, the K&N is the best of the bunch. Do you know for certain it was because of this the MAF failed? Or was it simply down to age of MAF and coincidence...? The MAF could still be the original after all, and therefore 4 years old...!

Scoobyslammed

Don't really know, but because there oil based I thought they didn't do the MAF's much good??? I thought the foam based ones will be better??? Dunno, anyone wanna advise me different...

SiHethers

K&N is the best of the bunch in terms of flow/filtration. It is only a prob if it has been over oiled (which is generally only a prob when the purchaser cleans and re-oils it, not when it's straight from the factory)

The blitz steel ones flow very well but don't filter, therefore break MAFs and compressor blades. Foam ones often still have some sort of oil impregnation to make them work.