The car my Daughter drives.
99 Auto, 4.0l. 170k miles. 4k since we got it. Needed work for more than a few things.

Have done a bunch of work with it...has a (worsening) problem.

Recently done:
New Carter (can't find a Bosch) fuel pump/sending unit (fixed the long crank issue).
Trans fluid change (and filter).
Oil Change
New Distributor/cap/rotor/wires/plugs/coil.
Cleaned Grounds.
New Crank Position Sensor (Mopar).
New Battery.
(bunch of other stuff not related to the powertrain).

The Fuel Pump was the most recent....before it was changed, it had a long crank, and occasionally, it would sputter/die/minimal backfire on starting. It would also very occasionally hesitate (almost stall) while trying to start out from a stop.

Fuel pump fixed the long crank, but did not fix any of the other problems.

So it's got an occasional stall (or bad hesitation) on trying to start from a stop while running (my daughter says she really has to punch the gas to avoid the stall if she feels it starting). And the sputter/die on trying to start. My daughter says it is worse on trying to start if she pushes on the gas.

No codes.
Actually drives very good, idles smooth, etc. once it's started. Just problems on starting initially (when cold) or when you go to start from a stop while running.

Any thoughts?

I do have a cheap Throttle Position sensor I'm going to try first (and if that is the problem, get a Mopar).

If it's a leaky injector, how to identify which one (or just swap them all out)?

 

A cheap or failing TPS can cause a stumble or stall. Check the vacuum lines and connections for any cracks, etc.. There is a connection under the MAP that is sometimes missed, so be sure to check that one. For the rubber bits, give them a squeeze and look for any cracks in the rubber. You cant always see them unless squeezed. Outside air can get thru the cracks and screw with the idle. A stumble or stall is possible. I had this with the Mustang once or twice and found a broken vaccum line. Fixed that and it ran much better. You can find new line and connections at the parts store. Its generic stuff (non Mopar), so you will have to mix and match.

I would remove and clean the throttle body and IAC as well. Remove the MAP and TPS and sit them aside. Use throttle body cleaner and the brush on the throttle body and IAC. Do not operate the pintle of the IAC, just clean the soot off it. A block of wood or whatever will hold the throttle open. They can get really dirty and end up with idle issues, and the IAC can get stuck.

Could be many things, but thats where i would start as they fixed idle issues in the past for me.

 

Underneath the MAP sensor is a rubber connector. Make sure that's in good condition. IDK if it's a serviceable item by itself or if you have to buy a MAP sensor to get one. I hope not!

 

This thread applies to my '98 XJ too.
It recently developed a hesitation, stumble or whatever you want to call it when I move off of a dead stop.

Not every time either and not unless you come to a full stop and the idle drops to its lowest point.

 

Although it's intermittent enough that it might still happen, but the Daughter says it hasn't done it in several days (and under the same conditions as it did before).

Still have the hard start (thinking that's the idle control valve, but I am going to also check vacuum hoses under the hood today/tomorrow when I get to work on it).

 

How about a code reader? Hard start I doubt has anything to do with the IAC motor. You need a code reader and a fuel pressure gauge to start diagnosing.

 

It's not throwing codes, and the only advanced code reader I have it a Schwaben (rebadged Foxwell) set up for BMW (I could get the chip for Chrysler products if needed), so I don't have a way to read live data.

The Fuel pressure was fine with the old pump (I do have a gauge)...I haven't tested the new pump pressure (but since the problem was there before and after the pump and sending unit swap, I can't rule out low pressure, but would it really be high on the possible causes list?).

 

Stalling and starting issues, yes its high on the list with a dozen and a half other things. It was fine before but you also have the regulator test, where it holds pressure for a certain length of time. Likely that was the problem with the fuel pump. but installing another one its always good to verify operation. Cam sensor, O2 sensor wire shorting up front, ...secondary ignition, , a few that come to mind

 

Clean them all out!!

 

Still have the hard start (thinking that's the idle control valve, but I am going to also check vacuum hoses under the hood today/tomorrow when I get to work on it).[/QUOTE]

Hey! My son's Jeep has the same prob as yours. Working on trying to figure it out as well. Your thread has been helpful! Question: I thought the new pump fixed your long crank/hard start issue?

 

Hey! My son's Jeep has the same prob as yours. Working on trying to figure it out as well. Your thread has been helpful! Question: I thought the new pump fixed your long crank/hard start issue?[/QUOTE]

Definitely.

I can lean in the car and crank it and it starts right away....no more priming the lines, etc.

I get the feeling I'm working on/was working on 3 different problems....the long crank (check valve bad...now fixed), the hard start (possibly the IAC or O2 Sensors I replaced fixed it), and the rough idle/stalling when starting from idle (maybe a vacuum leak or MAP sensor).

 

Definitely.

I can lean in the car and crank it and it starts right away....no more priming the lines, etc.

I get the feeling I'm working on/was working on 3 different problems....the long crank (check valve bad...now fixed), the hard start (possibly the IAC or O2 Sensors I replaced fixed it), and the rough idle/stalling when starting from idle (maybe a vacuum leak or MAP sensor).[/QUOTE]

​​​​​​Have similar things going on on my end. Appreciate your feedback. I'm focusing on the rough "cold" start... The new TPS you put in helped that?

 

I thought the cheap (bought it from Amazon a couple of months ago when we were working up the initial 'no start' that was the Crank Position Sensor...there's a Mopar CPS in it now). My Daughter pulled the old and put the new Throttle Position Sensor in. I thought that fixed the 'Stall when starting from idle' issue (but it just happened again). I thought the cold/rough start was more the Idle Air Controller...tried cleaning it, then replaced it, and the old one was stuck sticking out...it seems to start better (between that and new O2 sensors), but still have a rough initial cold idle.

Next up is the MAP sensor and do a smoke test for Vacuum leaks.