Faulty sensor? need help

[MarkLockyer]

So my car randomly started to just crank and not fire one day. It would eventually start and work fine, by leaving it or pushing it a couple of meters. But a week after it just never started so i had to walk home from work and leave it there. Today i was looking under the hood and tryed a few things e.g test if its the fuel and spark. I pulled out this cable (shown in pic circled in red) then plugged it back in secure and it started straight away. Just wondering what this is whether its camshaft/crank sensor or something different. It now drives poorly and idles poorly (exact same symptoms as a faulty cam/crank sensor). Any thoughts on how to fix this??

The yellow line shows where the cable leads to.

 

[bazeng]

That is indeed your Cam/crank sensor. (Cam angle sensor or crank angle sensor).

That is needed for any Efi engine to run.

Clean the pins, check for broken wires...
But it makes sense that if that was loose, you're car would not start...