So my '90 xj has been giving me some trouble recently... When in Park and it's on, it idles at about 1500 to 2000 rpm. Also, when I'm braking/coming to a stop I can hear the engine still running like I'm on the gas but am completely stopped. Then it'll push/lurch forward a bit. When accelerating through a turn it like to do a little lurch as well and will kind of pop (believe that one to be the trans mount).

What I'm wondering is what could the problem be? I've read that it could be a vaccuum leak, or a part of the brake booster, or the IAC valve. I plan on cleaning the IAC anyways so hopefully that'll solve the high idling but any other help on how to diagnose and fix would be great because the shops around here like to steal peoples $$.

 

Sounds like a vacuum leak, and those are usually a cheap fix, so try this first:
Find one of those small propane torches you can use to solder plumbing.
A can of starter fluid will work, but it's not as accurate and kind-a dangerous.
Shoot some unlit propane at all the vacuum lines and joints and fittings.
Don't be bashful, nohing bad will happen, get in close with the torch.
The RPM's will go up even higher when you point the torch at the leak and the propane gets sucked into the manifold.

 

Will a butane torch work as well??