Sounds like ISCV. its worth pulling all the other connectors off and cleaning them with some wd40.

I think you are meant to set the idle to ~600 IIRC with the ISCV unplugged. There is a little grub screw you set the idle speed with on the throttle somewhere.

The solution to the sump problem that we used (after 3 tries) was to rip the engine out

Good luck with it.

JAmes.