MY99 turbo uk spec wagon has developed an really erratic idle when warm, revs will bounce between 900rpm and 0 (basically nearly stalling). It starts fine and idles when cold, but wont idle when warm. Ive heard the 99 models had ecu trouble, is it possible it is the ecu?
Please help me a love my scooby too much for it to die...

 

Welcome!

You haven't heard quite correct re. the "trouble". The ECU is fine, the thing that tends to go wrong a bit on 99-00 cars is the mass airflow sensor (aka MAF or AFM).

If you have the option, get your car to a Subaru dealer and ask them to diagnose it, and they should be able to see within a few seconds whether the output from your meter is normal or not. If this is the problem, a replacement meter element is about £100. If yours is more than a couple of years old it might be worth replacing it as a precaution anyway - the part number is 22794AA010.

However, there are a number of other things that can cause or contribute to the symptoms you're reporting so it's worth getting it diagnosed before speculatively replacing parts. One thing you might want to look at is cleaning the idle speed control valve - search on here for how to do it.

 

Oh - a couple of further points. Firstly, and most importantly, don't drive the car under anything more than feather-light throttle until you have this issue identified and solved, as the consequences of driving under boost with a possibly failing airflow sensor will not be good for your engine.

Secondly, do you have an induction kit or aftermarket dumpvalve fitted?

Also, sometime later, someone will likely pop up here and tell you about a test you can use to determine whether your sensor is faulty, which involves starting the car and unplugging the MAF, and seeing whether the engine stalls.

This "test" is a Scoobynet urban myth, and doesn't prove anything, one way or the other. As such the best way forward is not to bother with it at all. As above the two ways to determine what the sensor is doing are either to monitor it, or to replace it, reset the ECU and see if the problem has gone away.

 

just to check that part number is for MY99 (last of the classics) sensor.

Oh and btw it doesnt have an aftermarket dump valve, and a green replacement element filter. Only other mod is a nur backbox

 

Last of the classics was MY00 - but that part number applies to both '99 and '00, yes. If you're going to replace it yourself (easy job, btw, if you haven't already looked at it), make sure you reset the ECU after.

 

Hi there, does it have any flat spots through the revs at all? Only reason I'm asking is cos my scooby a MY00 is doing exactly the same as yours, idles ok (ish) at start up but wants to cut out when warm. Thing is because mine has a flat spot at the bottom of the rev range (roughly 1000-1500) i assumed it would be plugs/plug leads/coil pack related??
I tried a coil pack an it didn't make any difference so i've just bought some new plug leads for it but now i'm wondering if i'm barking up the wrong tree??

 

You might be. Exactly the same advice applies to you as it did to Cables. Cheapest way to be certain is likely to be to get the car diagnosed, otherwise you could end up shelling quite a bit on a process of elimination - and go easy on the throttle in the meantime

 

Nice one cheers fella my mate's gonna ave a look at it for me on Monday he works at Subaru so he's gonna try a couple o things, MAF being one he also said it could be an injector, so we'll see what happens an I'll let ya know fingers crossed...

 

Well i went over to my mates today an turns out the leads i've bought don't fit (Bugger!!) they did say they are turbo ones but he reckons they're normally aspirated so they'll be goin back...!!
Anyway... he tested to see if one plug and/or lead was off by disconnecting one and earthing to the inlet, basically to see if it ran any worse, therefore (as the theory goes) if we disconnected a faulty one it would make no difference and run the same.... Sounds great but only problem is it ran exactly the same on every plug grrr!!!
Next thing in line (here comes your myth Splitpin) he disconnected the MAF and all of a sudden it runs like a dream!!!! (on tick over). So now he's convinced its MAF and it would be nice if it is but.. i'm not so sure cos isn't it running in safe mode then so therefore knocking out more than just the MAF??? Or is this just more b*****ks that i've heard off some1 on here??

 

i had exactly this fault on the same car,replaced loads of bits,ended up being the spark plugs!!!!,i still fitted a new maf for piece of mind,check your plugs.

 

Laughs, that's not the myth I was talking about. That one claims very specifically that you can tell whether or not the airflow sensor is good depending on whether you get a stall (or not) if you unplug the sensor with the engine running - with the myth going on to claim that if the engine stalls the sensor is good, and if the sensor is bad the engine will keep running. That one is dangerous bollocks because it can't definitively tell the difference between a sensor that is good and one that isn't, and, more often than not, it will pass a seriously degraded sensor as "good". Big problem.

However your situation is a little different - your engine didn't stall, and it didn't carry on running exactly the same either. From that we can deduce something.

He's likely to be right.

It will be in failsafe mode but your friend is probably correct to think that this is the MAF. The reason for this is that when you unplug it with the engine running, the ECU will run a timeout counter (of a fraction of a second) while it waits to see if the signal comes back within an acceptable max/min voltage range. If it doesn't the ECU will automatically substitute a "specimen" airflow value which is used to calculate the mixture - while at the same time switching off the boost, dropping the rev limit etc. in order to prevent the engine suffering damage due to the lack of proper airflow measurement.

Anyway, if your car idles stably with the MAF unplugged, this would point in the direction of your sensor being vibration damaged and its signal constantly dropping in and out - explaining why the idle will be all over the place, as one second the ECU will be getting some sort of voltage from the sensor, the next it won't be, then it will be, and, well, you can see how that works. Replace the MAF, ECU reset, and see where you are

 

it had a service so i new it couldnt be plugs and leads, i have replaced the maf and reset the ecu and it runs like a dream

 

Nice one Cables, good to hear it's back to how it should be

 

Having same sort of problem with my 2004 STi 2.5 US spec, was running like a dream but suddenly revs were up at 2000 and seemed to be taking in too much air. No CEL. Took it to Subaru - they cleaned the throttle head valve and it was running better but a couple of days later got very erratic throttle again, not so high but fluctuating from really low almost stalling to 1300. Back to Subaru who had another look at it and changed the MAF - that was 3 days ago. Now it seems to continue to rev on its own even though I take my foot off the throttle (very disconcerting) and goes back to near normal idle when I shift to neutral. I bought this car here 6 months ago it is a UK import and Subaru here (Athens, Greece) say might have been remapped in UK cos they can't read the ECU programme which isn't very helpful. Any ideas?

 

Hi guys sorry for the late reply (bloody christmas!!) anyway.. I got a new maf for my scooby, fitted it and it ran better but still wanted to stall (if that makes sense??) Plugged it in and all seemed well, MAF reading correctly.. in his words '..well it should run now!!' So I suggested cleaning the idle control valve as i'd heard about it on here, so he took it off cleaned it best he could (..outside in the snow!!.. what a guy!!) he moved it in and out a few times etc and put it back.
After this the car idled all over the place 4 a minute or 2, but then quietened down and ran perfect
Only thing is this only lasted a couple o days and i reckon the problem could be on its way back.. but its no where near as bad an dunt get anywhere near stalling so i reckon either a proper clean of the idle control valve or re-new should solve the problem.
Any tips on thorough cleaning, and checking etc for the idle control valve on here..???

 

No change to idle on mi scooby still garbage so i've taken the idle control valve off 4 cleaning but it seems really really stiff to move in + out by hand... Is it supposed to be like this or could it be buggered?
I've also looked at buying a new one on an cheapest i could find was $294 ... whatever that is in real money its a lot!!
So anyone know any tips or a decent method of cleaning em by any chance??
Please some1 help cos its doin my head in now!!!

 

Assuming that's US $, it's c.£185 at current rates.