monkeyneil

Hi! Sorry for introducing myself this way!

I've searched through here for hours trying to find an answer.

I've got a w reg forester turbo, uk model.

The other day it was driving as normal, just as i got home it would hardly idle and the engine light came on. That said a MAF problem, so i've put a new sensor in. The light has gone away and i've reset the ecu.

The problem is still there! I've tested another ICV and it doesn't fix it. The engine really struggles to keep alive when idling, however, when i pull a vacuum hose off the idle returns to normal.

Has anyone got any suggestions what i could try? Thank you very much!

STI_Baly

iTrader: (23)

Could you take a snapshot of which vacum pipe your disconnecting? As this will help. Maybe even circle it using a graphic programme.

monkeyneil

i've just pulled it off the standard recirc dump valve.

STI_Baly

iTrader: (23)

So this is the vacum pressure hose going from inlet manifold to Dump valve.

Could actually be a faulty dump valve mate. Have you got another you could try? This would also explain the eratic idle your experiencing.

monkeyneil

Yeah, its from the manifold with t-piece on. I've got a new forge VTA dump valve i've tried on it and its just the same

I really need this car going i'm supposed to be starting a new job in a week! Thanks for your help mate

STI_Baly

iTrader: (23)

I don't like the idea of there being a T-Piece on that hose mate, especially if it's going to a boost pressure gauge. Hmmm

The hose should directly come off the manifold and not distribute air anywhere else. It sounds like the Dump valve is staying open when idling which is sucking in air (on vta), therefore if it has an adjustment it will need adjusting.

Just extracted this from an old article i had laying around might help/explain things than my waffle.

At idle there is engine vacuum on the top of the Dump Valve piston trying to suck it open, and no vacuum or pressure on the bottom of the piston. Since a vent-to-atmosphere Dump Valve needs to be shut at idle to avoid air being drawn in through it, there is a spring inside a Dump Valve with the job of holding the piston closed. The spring preload adjustment is to allow for differences in engine vacuum from car to car, and variations in atmospheric pressure at different elevations.

On airflow metered cars the air drawn in through an open vent-to-atmosphere Dump Valve at idle would confuse the ECU and cause over-fuelling and stalling and in any case, the air drawn in is unfiltered.

Under cruise conditions (off boost) the Dump Valve is experiencing similar conditions to when the car is at idle, but there is less vacuum present on top of the piston because the throttle is partly open. If the Dump Valve spring has been adjusted to keep the piston closed at idle, it will also be closed at cruise.

On boost there is boost pressure on both top and bottom of the Dump Valve, the forces from which counteract each other, so the Dump Valve remains closed.

Not sure if the forges have adjustment. Have you got a after market boost gauge feeding off that T joint?

monkeyneil

all that pipework is standard mate, i've not touched any of that, on the forester it has and extra vac pipe to the side of the dumpvalve, which limits the boost as well as the ecu.

when i tried the VTA dump valve, it was working as it should with the piston moving only when sucked!

when driving it now, it feels different, it doesn't like to have more than, say 3/4 psi without it start to judder

STI_Baly

iTrader: (23)

Ok mate, well i'm pretty much lost with this one as i don't know much about the forester so am trying to answer this in a Impreza manner, hehe.

Neil your above statement is with the vacum pipe connected or disconnected mate?

monkeyneil

the engine is basically the same as the year 2000 on impreza engine.

I've not driven it with hose dis-connected yet mate

Does it sound like a leak anywhere? When i cover up the air intake it stalls though, I'm stumped, really am!

STI_Baly

iTrader: (23)

I'm assuming when you say you block the air intake your referring to the air vacum intake on the VTA DV?

Well if you block this your obviously not going to stall the motor, as there is no pressure keeping the dump valve closed mate. TBH honest mate i think you need to take it to someone who can do a visual on it, as it could be leaking hoses or it could be solenoid or anything else.

monkeyneil

I block the air intake - at the air filter, and it stalls, so that must mean there are no leaks in any pipes, right? wrong?

Can anyone help!?

monkeyneil

just dropped the kids off in it now. it feels like someone is pulling it back when you put your foot down, it doesn't have any pull in it, and it sounds different, kind of a flat sound, its hard to describe.

Could it be plugs on the way out?

but why would it idle correct with a vacuum hose off though?

Don Clark

Try posting in the European section at

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monkeyneil

update.

Just tried unpluging the spark plug leads from my central coil. It doesn't seem to make much difference when i unplug the one with number 1 on the coil pack. the one right under the airbox at the front drivers side. It does make a bit of a difference.

is this a common piston to break or is most likely the spark plug?

Just tried pulling off any vac pipe and immediately the car returns to normal idle, if i unplug 2 at the same time it stalls

rookymatt

iTrader: (15)

hmmm sounds like an airmass meter. do these run on substitue vaues if they are disconnected??? might be worth knowing before you disconnect it and put a fault code in the ecu.

monkeyneil

Maybe i have bought the wrong MAF sensor? it doesn't light up the engine check light though.

rookymatt

iTrader: (15)

you see if the sensor is wrong the car may be over fueling and the only way you are curing it is by adding extra air to the system AFTER the meter(pulling the hose off). on bmws (that's what i fix) disconnecting the airmass meter makes the car run a "substitute" value for the airmass, its bmws kind of a get you around but not perfect solution if you cant drive the thing with it on. i'd say pull that off and see how it drives, but i dont want you pulling it and then getting a mechanic to check the memories and with him seeing an airmass meter fault, jumps to conclusions. see if someone on here knows if there is a substitue, and if there is pull the plug with the ignition off and see how it runs.

monkeyneil

Sorted it!

I bought a new maf sensor and that took the engine check light off, but never fixed the car (as above) I was sure it was still the problem but no garage would beleive me. Finally got another one, and it runs perfect! so that was the problem all along!

Thanks for trying to help chaps

STI_Baly

iTrader: (23)

Glad you got this sorted mate, good luck with it now.

rookymatt

iTrader: (15)

Wicked, happy motoring mate!