4.0 Won't start / stay running

[jay79cj7]

My DD 00 XJ (4.0/auto/stock) failed to get me to work this morning. Luckily the CJ is pretty dependable. I'm hoping you guys can point me in the right direction and get it running again quickly because I need it this weekend.

It was about 30 degrees and sat outside overnight, so cold, but nothing like its been through here in N IL the past couple months. I went to start and it cranked over and over but would not run. It seemed like it was firing and just about to go, but wouldn't. I repeated this several times. Then I held my foot on the gas as I cranked and it fired right up. It ran very smoothly holding the RPMs up in the 1500-2k range, but as I took my foot off the gas it died. I repeated this several times and it would start to idle rough and die around 500 rpms or so. After holding it at 1500 for a couple minutes it would run rough but not die, with the tach bouncing around at the first tick above 0.

What would cause it to not be able to hold idle? I am thinking it must be some sort of sensor, but I am not familiar enough with the engine controls.

Thanks!

 

[tessa]

This may sound like an odd question, but have you checked your battery and alternator?

I had a similar problem with my Jeep in Dec (died, wouldn't start, then would start but would die if you took your foot off the gas, etc.), and it ended up being a bad alternator.

 

[SteelHeadz]

Possibly a sticky Fuel pump?, does it warm up in the afternoon ,if so have you tried starting it then?

 

[jay79cj7]

Thanks for the replies.

The battery and alternator are both about a year old, so they should still be good. The battery has cranked like a fresh one during -15 degree days, so it should have shown weakness then if it was going. The voltage gauge doesn't show anything wrong with the alternator lately, or when I get it running. I'll take a look, but I can't think of how that could be the cause anyhow... (Not that I am some sort of expert.)

The fuel pump sounded like its working fine, as best I could tell. I'm at work now so I won't have a chance to mess with it again until this evening. I would think that if it couldn't build up enough fuel pressure to idle, it wouldn't be able to run at higher RPMs. I checked my fuel pressure about 2 months ago, but I'll check into that again.

I'm reading about IAC. That seems like a suspect since it controls the air flow into the intake when the throttle is fully closed. If that got gunked up and stuck, that could cause my problems.

 

[SteelHeadz]

Thats a possibility that you can easily verify..

 

[Edge]

Verify how?Maybe thats what I'm chasing as well.

Edge

 

[SteelHeadz]

Remove the IAC and look into the port where the pintle sits in and the IAC pintle as well, if you see a lot of carbon build up, clean it with a Carburator cleaner.

 

[jay79cj7]

Cleaned out the IAC and its housing Friday night and all is well.

 

[thedevil1236]

i had that problem too. one keep my updated on what you figured out. the dealership replaced the battery and it fixed the problem. i really dont understand how it works at all and why thats the solution...so very confused hahaha