2019 Volvo V8 380 C-M won't start unless i give it throttle

[websterama]

Yes

Ok, so i went over every inch of the harness I could get to, and it all seems intact, clean, and not in physical contact with the manifold anywhere.
I did, however, find something interesting in doing this trace. On each manifold, there is what I assume to be one sensor, that screws into the top. I'm guessing that's a temp sensor for the manifold itself.

One of them was flush/tight. The other one (on left) was really loose. Like so loose that I was able to hand tighten it back down and it took 4 or 5 full turns to do so. I've attached pictures of them here (pre-tightening). You can see the first one is flush and the other one not at all.






Now this is probably magical thinking on my part. But after tightening it down, I went and flipped on the battery switch, turned the key, waited for it to prime, and it fired up on the very first try. Took it out for a spin in the harbor to let it warm up for a bit, got up to 2750 RPMs, came back to my mooring and turned it off. Hung out for a bit, ran my blowers and turned the key on again. Primed faster than usual (maybe because warm) and sure enough, fired up on the first try again.
Like I said, probably magical thinking to believe that a loose screw on a sensor into the manifold would be the extent of my issue, but it's the first time I've had the boat start twice without any shenanigans since I got it transported here.

Anyway, I didn't see any other weirdness in the harness anywhere else I checked and I was able to get pretty good looks at most of it.

 

[muc]

Yes that’s an exhaust manifold water temperature sensor. And no it couldn’t cause the issue you’re having. I don’t know why it wasn’t seated. It screws into a blind hole so no water would leak and I don’t think it would affect the operation of the sensor.

The problem with inspecting a wiring harness is that the problem is almost always in the place that’s hardest to get to. I have had some that I couldn’t see the damage until I had removed it from the engine. And one that I had to untape to find internal damage.

There is a possibility that you moving the harness around made the problem go away temporarily. Or it’s just an intermittent issue that will keep coming and going until someone fixes it.