Bad cold start Z20NET

FLC

Hi all,
I am looking for help. My Vectra C z20net 2007 has problem with cold starts - when stay 2-3 days in garage.
After turning key to start engine I feel a vibrations coming from the engine + knock sound and engine looks like to shut off (die). It is only for a few 5-8 seconds from start, then choke off - rpm sit on 850-900 and everything is ok.
I drive to work - car stay 9 hours on 1 place, then start - everything is ok. If it stay over weekend start problem appear.
My steps : throttle body cleaned, chain tensioner is ok, new oil + filter, diagnostics displayed no fault codes.
Can someone help me, any tips or hints ?
Thanks in advance.

vocky

might be worth checking the fuel pressure regulators, sometimes they can cause issues like yours.

FLC

thanks for advice. I will seek where they are and check them, but if the regulators are wrong - problem will appear whenever, no only parked vehicle, don't you think ?
I have idea about camshaft position sensor or engine cool sensor - sensor displays wrong temperature - ecu / pcm think that engine is warm and prepare poor mixture air/fuel for cold start. Air to fuel ratio is not optimal. What do you think about this ?

vocky

the coolant temperature sensor is cheap, about £20, so worth replacing anyway.

Logically the cam sensor would play up all the time too.

Other than that it could be the chain tensioners draining of oil, might be worth an engine flush, then new oil + filter.

David_Dixon

As Vocky says, I think I might be tempted with the CTS first!

FLC

Chain tensioners already checked and oil +filter replaced recently. So I'm going to check fuel pressure regulator and then will replace cool temperature sensor.