mk2 golf gti 16v kr. vacuum at block breather

[martinws]

Would this not cause unmetered air to enter the engine if the breather is exiting below the metering head?

[Monkeymagic]

No the air comes in under the flap and it is lifted by engine vacuum. It rough when disconnected because air is introduced into the intake manifold.

[Monkeymagic]

Right this particular car is doing my head in.
My mate has said that the cold idle has a mind of its own.
It was revving itself to 3000 rpm. I just assumed it would be the co. I checked it again ignition timing is smack on.
I set the co up again and it seemed fine. Another call tonight. Its holding back and coughing.
I noticed though that the switch on the throttle body was not be switched on. This is the switch which tells the isv to kick in. However even when the throttle is open the isv is buzzing. Something is very odd.
Anyone wish a kr that can test their isv surely it should stop buzzing when switch is off.

[Rusty]

Has he fitted a KR exh cam in the inlet and not timed it properly?

Temp sender could be the issue, check the resistance

[Monkeymagic]

I have never heard of anyone fitting a kr exhaust cam to the inlet.
All 3 switches on side of head are the same part. 2 control isv ecu and 1 does temp gauge. Ill try testing them

[Rusty]

Fairly common mod but has to be done properly... Unlike a KR I chased an idle problem on for ages... OE cams back in and worked perfectly.

[Sleeper_Avant]

like i said i chased this for months with my 6a and it was down to switches and incorrect fuel pressure.

just because the base idle CO is within tollerance doesnt mean its all good mate.

have you smoke tested it for leaks aswell?

[K Simmonds]

I checked my breather today and mine is not in vacuum, there are most definitely fumes coming from the crank case. I'll take a look at the ISV tomorrow.

[Monkeymagic]

Thanks mate.

[Monkeymagic]

Just one thought. K does yours have the small bore pipe going to the inlet.?
Im now thinking i replaced this breather pipe as it was split. Im wondering if the increased vacuum acting on the lower half of metering head causing it to try to close the meter Flap.
On cold start the control pressure would be affected. All this started after changing the pipe.

[K Simmonds]

Sorry for the slow response, only had a chance to take a proper look today. My breather does have the small bore pipe connected to the underside of the inlet manifold. If I blip the throttle the breather does go into vacuum slightly but at idle there is definitely gas coming out. My idle valve is having a wobbly at the moment so I can't say with 100% certainty what it's supposed to be doing but as a rule it only buzzes as you lift off the throttle in order to catch the engine before it stalls and settle it to decent idle.

[Monkeymagic]

Well my tiny mind has been in over drive with this. My theory was that the breather pipe was applying vacuum below the meter head flap pulling in past it's stop. The natural intake vacuum is trying to lift the meter flap.
At idle on cold the control pressure is reduced to allow the flap to lift more thus rich ending mix.
However the two vacuum act in conflict causing idle to be all over the place.
I started the car from cold today it was bouncing between 400 and 3k.
I then checked the car was venting from the block it was. I then clamped the T off and started the car. It ran sweet the best I have ever known it. The PVC hose was venting to the air box under positive pressure as normal.
As a temporary measure I blocked the small bore hose I checked the co and the screw acting as normal clockwise to richer anti to lean out.
So all I need to find out now is why there is so much vacuum acting on the pipe.
I suspect the injector shrouds have fallen to bits and somehow they are allowing too much intake vacuum to act on the small bore port ......????? It's a guess but the best I have until I dismantle things but I'll get the seals and shrouds first. The car runs and goes really well and the slight hiccup on idle is gone too.
I'll result it once shrouds replaced.

[rj scotty]

Please let us know your findings, really curious on this one.

[Monkeymagic]

I will. I strongly suspect the injector shrouds and seals separate channels in the intake./head. By replacing the split breather it increased the vacuum and highlighted this issue.
Club gti has been useless for advice. I'll get it done I'm sure.

[Rusty]

Sounds like there's a 1 way valve or similar thats missing / defective.

The metering head flap has minimal pressure difference over it, a few mBar. The throttle body causes the vacuum and the metering head flap is actuated by the air entering the engine.