1990 XJ has very rough idle. complete tune up was done 2 mths ago including new wires. After we drove to CA from CO the RPMs drop to almost nothing at a stop light and stalls most of the time. All vacuum lines seem fine but I could be missing one? Exhaust note is VERY loud kind of like the muffler is off but it is fine. Any ideas out there what might be wrong. I am kind of a newbie when comes to these things my dad usually handles them, but he is back in CO.

 

Do a compression test on the cylinders.. you can do it or have a shop do it.. the job is fairly eaisy and all you need it a compression tester that you can rent from autozone..my 93 country idles rough and low.. come to find out i have really bad compression in #1 cyl..thats my problem i dont know about yours, just a thought...