I have a 2000 XJ that was occasionally have a little stutter in its idle. I tried cleaning the IAC but ended up breaking it. So I installed a new one. Now it will barely start and stay running on its own. If I just barely crack the throttle open it will fire right up. I have to keep my foot on the gas for about a min or so (its cold here in CO) until it has warmed up a bit and then it is fine. It restarts fine on its own as long as it is warm still. I also replaced the fuel pump last weekend with a new Bosch. I am still losing fuel pressure after a few hours to the fuel rail. I am guessing maybe I have a leaking injector.

 

1. Have your battery "load tested". A marginal battery gives the engine management system fits and can create a symptom of stalling at idle until it warms up a bit and the alternator charges the battery enough so as to keep the engine management system happy. Life starts with electrons for automotive electronics. Deal with this first.

2. What brand IAC did you install? I recommend only MOPAR IAC sensors for the XJ. You get what you pay for. Did you clean your throttle body when you installed the IAC? Pretty important. They get carboned up over time and miles.

3. If you are losing fuel pressure after installing a new fuel pump, yes it's possible that you have a leaky fuel injector, especially if they are original. There are some very specific fuel pressure tests that can be done to isolate this. See below.

4. Do you have a check engine light on or have you seen one? If so, you must retrieve codes from the computer for clues/guidance.

Good luck and keep us updated!
---------------------------------------------------------------------
If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.

Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.

Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.

*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood

*Start engine and bring to normal operating temperature.

*Observe fuel pressure gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)

*Shut engine off.

*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.

If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the
fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose normally included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, but here is basically how it works:

*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.

*If the pressure remains at 49 psi for an extended period of time then the problem is in the tank – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.