I've been away from the forum for a few years, and sadly my xj has sat almost entirely used for close to 2 years. It has fallen into disrepair and I have my work cut out. When I got it starred a few weeks ago it was idling very high. When I first start it it runs for a minuet at normal idle then slowly steps up until it's roaring at around 2k rpm when I put it in gear it drops down to normal rpm again. My first thought was idle air valve but I'm not sure if I'm right. Other issue is that it has a CEL for the first time in the 4 years I have owned it. Was my first instinct right and it as simple as the idle air?

 

I would check the code first. It could be unrelated or it could tell you exactly the problem.

 

check the vacum canaser for bad hose

 

I have checked the codes and I got a code for iac and TPS I replaced both and it still idles around 2200 rpm checked codes again and the TPS is gone but the iac remains. As car as I can tell all the vac lines are fine. The canister lines and the purge valve lines all look fine. I'm at a bit of a loss on where to go next. Could a bad seal on the intake manifold to the head cause this?