I have got an old heavy duty cast iron pan with removable wooden handle that I could never cook properly with.
I spoke to Derek F off this forum who is a chef and this is what he said to do, since I followed and did what he said it has been perfect and is all we pretty much use now..
------------
First thing is to get them cleaned as good as possible. You are trying to get them back to a raw porous looking cast iron surface. Probably a major wash in soapy water then put on an element or gas and get hot for some time, say 30 mins.
The crud that is fixed to it will become a bit flaky and you can work towards scraping it off. Metal spatula on the flat one, wire brush on the other.
When you think you have it properly done (will look dull and porous)
Remove handle and put them in a preheated oven 280C with a light layer of vegetable oil or melted shortening for about an hour.
Let cool, then wash out under plain hot water put on the element and work in a light coat of vege oil with the spatula ....it should end up looking shiny and sort of smooth again.
Should be good enough but you can repeat things until you get it perfect.
From then on, when using, heat the pan and a smidge of oil or fat before the food goes in. And I only rinse the pan under running hot water.
If all is right eggs or cheese will not stick.