Hey there.
I'm new to this forum, just going to start firing questions.

My cherokee won't run smoothly enough.
It starts up OK, idles kinda' roughly when it's cold, nothing major but could be better, but it's when I drive off that things start bothering me.
It drives good, and it's not like it's dying on me or anything, but it stalls a bit when it get's to ca. 2000 rpm and up to about 2400 rpm.
I've changed the spark plugs, spark plug wires and two other things connected to the wires that I don't know what are called in English (as I'm from Iceland).
That didn't change anything.

What are my next steps? I have a new fuel filter, still in the box.. but if it was the fuel filter it would stall all the time wouldn't it?

 

Put that fuel filter in regardless. Good preventive maintenance.

Here is a link to testing of a lot of things on your RENIX (87-90) A good bookmark.

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

Verifying proper fuel delivery would make sense. Hook a fuel pressure gauge up to the schrader valve on the fuel rail. At idle, you should have approx. 31 psi at idle. Then disconnect the vacuum line to the fuel pressure regulator (be sure that line is pulling good vacuum) and the fuel pressure should jump to approx. 39 psi. If you don't see these readings, you have a fuel delivery issue.