2014 Skoda Octavia VRS starting issue

Hi.

Over the last month, I have been doing a number of cosmetic and engine related jobs to a 2014 Skoda Octavia VRS MK3 with the 2.0L Turbo Petrol engine from the MK7 Golf GTI.

The issue is that when the car starts, it immediately stops. It is most likely caused by myself when reassembling some engine related components. I had this issue a couple weeks ago after reassembling some of the engine and I had forgotten to plug the wire loom into the fuel rail line. This issue feels exactly the same except I cannot work out what I did wrong this time.

Since the car was working about a week ago I performed an oil change, replaced the intake manifold sensor, and replaced a transmission coolant valve. Was pretty familiar with these components as I previously diagnosed all the issues. The good thing is the new parts got rid of the OBD codes but I haven't got any new codes despite a new issue.

I loosened some of the fuel lines before and after the high-pressure fuel pump. Fuel sprayed out of both of them, maybe a little less pronounced when I did it after the fuel pump. However, fuel was under pressure either side. Everything appears to be plugged in.

To make matters more difficult, I currently have a dead battery so I have jump start it. To rule out the battery as the cause of the issue, I temporarily put a good battery from a 2014 Audi A3 (same MQB platform and engine) in the Skoda and still getting the same issue as when I jump start.

I don't have OBD11 or VCDS. I do have a Launch CRP129X.

Any help is much appreciated!

The symptoms suggest an immobiliser issue, is the key warning on in the dash?

Thanks for the reply. A few people have suggested the immobilizer, but I don't have a key warning on the dash

Edit: Just checked the manual and it doesn't seem as if there is a light (key) for the immobilizer

Any suggestions?

I think there is, the Launch should tell you if there are codes in the engine ECU and dash for an immobiliser problem.

Thank again. It seems the new sensor for the manifold I had bought online was faulty. As soon as I unplugged it, I could start the car with no issues (with the battery from the Audi).

Chinese Replacement Auto Parts?

Just came across your post from 8 months ago. Man, that sounds frustrating, especially after all the work you put into it. I'm hoping you've managed to sort it out by now. If not, or for anyone else stumbling upon this thread with similar issues, I'd recommend checking out this resource from https://stuck.solutions/. It has some handy tips and guides that might help pinpoint the problem.
Given the thoroughness of your diagnostic work, it's a puzzle why the car's behaving the way it is. Sometimes it can be the simplest thing that you've overlooked, like a ground wire or a sensor plug. Did you get to use your Launch CRP129X for any error codes?