Pulling my hair out - G60

Hi all 

Ok so here goes

I have an issue with my G60 

If you start the engine it will idle at about 1100rpm then once you rev it, it will idle at 2000rpm or start to hunt 1500 - 2500rpm. If you switch it off and restart it will go back to 1100 rpm until it's revved again.

So what I've done so far

New parts 

02 sensor Bosch 4 wire
Blue CTS  genuine
Dizzy cap and rota (not to fix this fault just part of doing a service)
Vac hoses (ecu - clock for) 3.5mm 1meter for the ecu
Idle screw

Checked the timing and adjusted the dizzy via a timing light

I didn't carry out the conversation however after giving it the once over - 2x normal relays are being used for the fuel pump and ecu (all seems to be ok)

The old idle screw was chewed up so I ordered a new one however the old one is different looks to be a gti one and not a g60 one. However I'm not convinced that the new one is sealing either.

Once running and I disconnect the cts and rev it 3times it doesn't matter what I do with the idle screw to doesn't mate any changes 

However at this point the idle drops to 900rpm

If I block off the isv it will hunt like mad and you can hear it back firing through the inlet manifold (or pre detonation), again no difference when adjusting the idle screw.

The 02 sensor has a good ground - however tracing it back to the ecu (purple and black wire shielded) the purple going into the ecu but the black just ends in the ecu plug and doesn't go anywhere

You can hear the isv clicking with the ignition on (have a spare and it's the same with both fitted)

Throttle switch's both working

02 sensor seems to be fixed at 1v watched it for a minute and it didn't change

I'm getting to my wits end with it, 

My thoughts are the following 

Possible air leak, manifold gasket is pretty much the only one I've not replaced

Ecu issue 

I hooked it up a to read the blink codes and got the following 

Air temperature circuit
Idle switch circuit
Cts circuit
02 sensor circuit
Internal ecu fault

However none of these code would clear and I'm not 100% that all these can fail at the same time, unless they are all wired internally to a common on the ecu

Any help would be much appreciated   

Just my 2p worth, have you put the correct grade of oil for that engine type? Thicker oil could at times cause this type of behaviour.

I remember my uncle had a Yaris, and it was revving like mad, after spending alot of money investigating, it ended up being £15 of correct oil grade.

Good luck and hope you find the issue