Here's the thing, all breathers on petrol engines go to the high pressure side of the throttle butterfly otherwise the engine would be pumping air into itself, with the engine idling there is no vacuum available to create negative pressure, it's only once the throttle is opened that there is a depression available to help evacuate the crankcase. Pull the breather hose off the airbox and watch the smoke coming out if you don't believe me.

 

All this is a red herring anyway, the OP's fuel economy is excellent which it most certainly would not be if his breather were blocked.

Here's the thing, all breathers on petrol engines go to the high pressure side of the throttle butterfly otherwise the engine would be pumping air into itself, with the engine idling there is no vacuum available to create negative pressure, it's only once the throttle is opened that there is a depression available to help evacuate the crankcase. Pull the breather hose off the airbox and watch the smoke coming out if you don't believe me.

All this is a red herring anyway, the OP's fuel economy is excellent which it most certainly would not be if his breather were blocked.

Not the case, I don't think (will check on the Polo at lunchtime, but 99% certain it's downstream). The PCV valve self-restricts the connection so that at idle the passage is very small, so the 'pumping air into itself' is minimised with the deep depression in the inlet manifold at that time, but fundamentally that is exactly what's going on at other times. The connection to the airbox is sucking, not blowing. Positive ventilation, not positive pressure.

This is the 3-pot system (with a minor error at the bottom where they say 'oil' filter, should read air filter)

The system on my 2003, BBY Polo is the same except the non-return valve is on top of the rocker cover, and PCV/vortex separator is in a plastic lump on the rear of the block.

93k on the clock

Not the case, I don't think (will check on the Polo at lunchtime, but 99% certain it's downstream). The PCV valve self-restricts the connection so that at idle the passage is very small, so the 'pumping air into itself' is minimised with the deep depression in the inlet manifold at that time, but fundamentally that is exactly what's going on at other times. The connection to the airbox is sucking, not blowing. Positive ventilation, not positive pressure.

This is the 3-pot system (with a minor error at the bottom where they say 'oil' filter, should read air filter)

The system on my 2003, BBY Polo is the same except the non-return valve is on top of the rocker cover, and PCV/vortex separator is in a plastic lump on the rear of the block.

 

That explains it; the PCV valve is pulled open when manifold depression is strong, when it drops the PCV valve closes, the NRV simply supplies air on demand to equalise pressure.

 

On your BBY and my AUB we have a much simpler system where the plastic box on the back of the block is a combined labyrinth and flame trap returning oil to the sump under gravity and the breather pipe goes straight to the airbox to equalise pressure.

 

In any event the OP's breather is unlikely to be blocked.

Well, not really. The PCV valve (on both the cars I have to hand, Fabia and Polo) works oppositely to what you've just said, and my BBY is just like the 3-pot diagram above with the exceptions noted in the sentence I wrote below it. Below-throttle vent pipe from breather box into manifold, just as in the diagram. I guess your AUB is from an earlier 'take' on these where emissions regs weren't so tough, and things were arranged a little differently. I guess I'd expect an MPI to be more similar to yours, due to vintage?

 

Whether there's relevance to the OP's car I don't know, TMB suggests it should behave like my Polo when all is well, but without detailed info/pics of the MPI system I can't really say, other than to observe that he's a damn helpful fella who wouldn't mislead deliberately.

The breather on the 1.4 mpi goes from the oil cap (which usually doenst seal properly when thr engine cover is fitted) up to the intake pipework before thr throttle body.

None the less i think this has gone slightly off topic.

And you have my apologies for the topic-wander.

 

How's the improvement in the warm-starting? Has it been maintained since your 'reset'?

Started fine yesterday morning. drove to london and back bpth cold starts so haven't had a chance to test it warm

Fault found, using my fault code reader measuring real time data i found the pre cat lambda sensor (b1s1) measuring a fixed 1.275v doesnt vary at all.

Good news, glad I could point you in the right direction.

 

Apologies for the tedious combat between me and wino, we love each other really, it can happen when keyboard warriors clash  :peek:

:clap: Sepulchrave nailed it in a sentence.  Edit: earlier in the thread; and there ^.

Changed it with a spare (old one) but stayed at 1.275 Volts. would appear its more likely a wiring issue because it stays at that voltage whether i have either plugged in, or have S1B1 completely disconnected, it stays stationary.

Forgive my ignorance, but is that sensor wideband or not on your car. I'd guess not?

its a 6 Wire (4 excluding the two for the heater) so i pressume it is a Wideband yes.

 

Its a later emission standard so has O2 sensors, the earlier emission standards only had one.

Ah, thanks. Is the connector pair quite near the ground? Any sign of water ingress?

I guess if there isn't any such visible evidence at the connection it's initially a case of buzzing out each wire back to the ECU. (Thinking aloud/stating the obvious).

Thats my plan, my Alfa Romeo maintenance is taking priority so this will be on hold for a week,

Year and engine code of the car? I can probably find the wiring info for you if useful?