Hello everybody!

I have an 1986 Mazda B2000 which was running fine, but now all of a sudden has a rough idle, it seems like some cylinders are not working. When rough it also smokes and seems like unburned fuel exits the exhaust.
When driving and on higher rpm-s, everything is fine.

My first thought was that egr valve was stuck open, so on the lower rpm-s the fuel was too rich and could not be burned.
On my truck the egr looks rather different than everything I found while googleing. It seems to have 2 membranes instead of one. Part no Mitsubishi K5T515 88. I tried googleing the vacuum diagrams as well, but I did not find anything which would include an egr with 2 membranes.
So I removed the valve and disassembled it, it goes without saying that it was very dirty, so I was confident I found the problem. I cleaned it thoroughly and put everything back together, but the problem still seems to exist.
I also tried removing the hoses from the membranes while running, it seemed to have no effect.

Are there any suggestions what to try next?
I am thinking of blocking the opening where egr goes into intake. That way I should at least confirm whether it is egr related or not.

Thank you in advance!

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