Loud KNOCKING / RATTLING at cold start up? Any ideas?

[SoCalFZJ80]

I experienced the same problem for the second time myself yesterday. My 80 had been sitting a week on a slight decline. Hard start accompanied by a loud knock & rattle. After about 5 -10 seconds of cranking the engine started and smoothed out. Running Rotllea 15W40 with Toyota filters. Starts every time normal since and runs as it did before. The first time this happened was a few years ago after it had been sitting a few weeks.

 

[Shoredreamer]

Did it happen only while starting/cranking or also with the engine running/idling. If it’s only when cranking to start, I had a similar issue that made a loud rattling knock noise. It also illuminated the CEL light and found it to be a Code 12. Replaced my original starter and no more rattling knock at some start ups. Happened maybe 1 out of 10 starts, usually cold. Engine runs perfectly fine after that.