EP6 / Prince engine unstable idle when cold

[jcmnz]

Hi, I have 'problem case' C3, 2011 1.6 non-turbo prince engine. Originally it had a 5FS engine that died, I purchased it and transplanted a 5FW (yep...and mucked around installing the controlled oil pump...working fine). Once warmed up, it drives/idles superbly, but when cold starting although it fires into life, it gets stuck in a unstable loop trying to regulate idle. If I manage to catch it out and get some revs on as it fire, hold at 2000 for a few seconds, it then settles down and is fine. When in the unstable idle state, it doesn't respond to accelerator pedal; with diagbox connected it reveals the variable lift actuator is the only thing oscillating back and forth trying to control idle speed. Plus accompanying engine fault warning. There is a persistent fault code that is just labelled as 'internal' ECU fault. Once, I reset all the learned parameters - that did work once, when cold, but problem came straight back.
Any ideas?! I still have the old engine, so I can scavenge actuators and sensors. This car has sat for two years, so fuel may be getting stale....as a long shot!
Thanks

[GiveMeABreak]

This topic has been covered several times - I suggest you have a read of my post here:

viewtopic.php?p=693449#p693449

and posts here:

viewtopic.php?p=725074#p725074

[jcmnz]

The oil pump stuff doesn't seem to be the issue - the target and actual pressures are tracking nicely, and stable, so I've no reason to think that's the cause of the instability. My question is really general Ep6 engine related - what are likely culprits for odd behaviour - there's lots to go wrong! The Variable lift is just going crazy. I could try swapping sensor/actuator I guess.

[xantia_v6]

Monitor the actual and reference air values and see how they are fluctuating.

[jcmnz]

I had a session with DiagBox last night. From cold, car fires up straight away and enter the oscillating idle phase (and is unresponsive to accelerator pedal). Reference filling and measured filling dancing all over the place.
https://photos.app.goo.gl/8LoMJozGypt7uF7QA

After running like this for 10 minutes or so, it'll restart and be happy-ish:
https://photos.app.goo.gl/6fTJ5H4pxyFcuyXQ7
I observed the oil pump was happily under control, reference and measured pressure were stable (around 3300mbar from memory), and would be seen to be tracking up and down with engine speed.


I've never seen it before, but after some running, the ECU showed a permanent fault on atmospheric air sensor.

And although looking settled...the oil pressure has gone sky high (5195mbar):

Ref pressure seems wrong - and the control loop is doing what its told - solenoid drive zero%, trying to control it.

....but the oil pressure reference value also looks wrong - perhaps as a result of the atmospheric pressure reading being odd:

How many air pressure sensors are there? I thought there was just the one - inlet manifold.
Any red flags from the above pictures? It seems like just one thing is likely to be wrong....Also of note; I used to get P1667 ECU internal fault (permanent) which has now disappeared!

[xantia_v6]

I would expect that there is an atmospheric sensor, maybe part of the throttle assembly.

The oil pressure readings do seem strange. I think that it would be worth checking the 5V reference voltage that goes to the sensors, and check that it is not fluctuating.