Breezy_Pete

My policy with repairs is to fix each evidenced problem as they become apparent. If the overall situation doesn't improve, look for the next bit of evidence. Quite often the first repair is sufficient, without it necessarily being clear why. I'm not sure that the thermostat was ever misbehaving. If the engine ECU was getting unreliable temperature info, it can't control things correctly.

It says 2.25C, I think. Which may be consistent with no flow through rad at that stage. So radiator outlet temp sensor probably OK, main engine one not so good.

Z19 is the heater within the pre-cat sensor. It gets 12V from the blue/red wire at the bottom of the diagram, ground side of it is PWM'ed by the engine ECU via the brown wire going to ECU pin 5.

I'm reasonably sure that the cap doesn't touch the baffle.

Fit cap in this orientation: Turn 90 degrees clockwise to lock down.

Pics now visible. Hopefully an owner with same engine code may be kind enough to provide a comparison photo. I can get a shot of the earlier generation equivalent in an AZQ-code HTP engine once my partner returns from wherever she's just gone to.

Annotated pic showing some PCV parts; orange rectangle contains cyclonic oil separator, pink rectangle is PCV valve. I think what you're seeing with cap not present is just a baffle to stop oil being flung continually at underside of cap when engine is running.

Your pics aren't showing. I don't think there's any part of the PCV system directly under oil filler cap.

I'm happy for you.

Just to balance some questionable assertions...

How many miles has it covered?

Try disconnecting and reconnecting the battery again, with a 2 minute pause between these actions.

Can you provide a link to an example, please?

There's quite a bit of info about the PCV system in page 2 of my thread here: https://www.briskoda.net/forums/topic/531352-petes-rescue-roomster/page/2/ Keep going until you get to the part (post on 21 June) showing the valve in the intake manifold, which is a part that will rarely be working correctly in older engines, I expect. The whole PCV system is a little complex on these engines, involving internal cast-in connectivity, external hoses and valves, and pathways and valves within the plastic oil separator box. Workshop diagrams and several photos can be found in the linked thread.

Yes, part number same as Lee says - 1K0 906 627B "Pressure converter"

Looks like I was wrong about push fit. Top work Lee. If I had the VIN I could see if that part number is a match. Message sent.

From the photograph it looks like that's just a push fit in the bracket. Pull it free and read the part number that will be printed on it somewhere.

I was thinking that maybe a charcoal canister full of liquid fuel could be causing the 'system too rich' fault. Each time the purge valve opens to clear fuel vapour, much more fuel than expected by the ECU may be coming through. It just seemed possible when you mentioned the over-filling of the tank recently.

It will be easier to remove the servo end of the old one if you deplete the residual vacuum by pressing brake pedal a few times first. A bit of saliva as lube on the new one will reduce the force required to insert that end. Other (inlet manifold) end may have a metal clip on the original, not sure. As long as new one is a snug fit that can probably be replaced by a cable tie, or small jubilee clip, but don't over-tighten, the spigot is plastic.

Any rust on the outside edge will also add to measurement error, unless scraped off back to parent metal beneath.

Is the thing you're measuring with going across the sticky-outy bit in the middle? If so, cut a u-shaped piece of cardboard with a 312mm gap between the legs, and use that as a makeshift caliper.

Crank sensor is round the back of the engine block on the htp engines. Approx where this ring shows:

Front brake PR codes do not tend to appear on the boot sticker.

No. There's no pressure sensor, just a pressure switch. That's either on or off, earthing the wire that goes to it, or not, either side of its threshold pressure. Chain timing checking is a bit awkward on this engine, really needing the locking tools to be fitted in place of crankshaft and camshaft sensors. Cam sensor is very easily removed, crank sensor is far from easy to access.

Possibly the thing hasn't remained in the correct installed position, such that its hot bit is leaning on plastic housing?