I have a 2000 xj classic, 128,000 miles , all stock. It requires me to blip the throttle on start up. When it's idling there is a whistling sound that I cannot locate. I've changed the TPS and cleaned the IAC valve. While cleaning the IAC, I had to disconnect the vacuum hose at the manifold. Started up like brand new, although idle was a little high. A day later I realized I forgot to hook the vacuum line back. While running, I reconnected the line and the engine dies! So, no improvement other than Advance Auto's bottom line.

Please help!

 

Id say the whistling is from the little air restricting thingy most people take out of the air box tube. Pretty common thing to do lol