4.0 XJ wont start or Idle by itself without the accelerator pressed when cold - JeepForum.com
 
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post #1 of 10 Old 01-16-2008, 01:24 AM Thread Starter
L20KEV
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4.0 XJ wont start or Idle by itself without the accelerator pressed when cold

I have a 1998 4.0 Xj and yesterday it would not start with out the gas and when it did it would instantly die unless you keep the gas on. after 5mins it idles/drives perfectly and is fine until it gets cold again.

Any suggestions?

the only other thing it has problem wise, is the cat box has rattled inside for the last 6 months. The check light, light is fine.


Last edited by L20KEV; 01-16-2008 at 03:15 AM.
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post #2 of 10 Old 01-16-2008, 07:50 AM
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check the fuel filter, could be slightly blocked. Check the linkages on the TB, clean the IAC.

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post #3 of 10 Old 01-16-2008, 09:06 AM
CJ7-Tim
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Quote:
Originally Posted by L20KEV
it would not start with out the gas and when it did it would instantly die unless you keep the gas on. after 5mins it idles/drives perfectly

Have the battery load tested at a shop or auto parts store. You have the classic symptoms of a bad battery or corroded battery connections. When the battery goes dead or when one of the cells goes bad and you have reduced voltage, the engine computer forgets the idle settings. After 3-8 minutes of running or driving, the idle settings are re-learned. Your battery may have enough power to start the engine but the computer is sensitive to low voltage.

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post #4 of 10 Old 01-16-2008, 09:16 AM
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this is from the fsm on my 2000, but 98 should be about the same.

the computer is rated for 8 volts and will lengthen the injector pulse to compensate for low voltage (it monitors battery voltage for this purpose). in theory it should run fine till it drops below 8 volts. also when cold (open loop mode) it ignores learned idle settings and uses hard coded preset values. once its warmed up it will use the learned settings.

sounds like the cat or IAC maybe.
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post #5 of 10 Old 01-16-2008, 10:26 AM Thread Starter
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Thanks for all your advices

whats the IAC?

As the cat is rattling i wonder if a part has broken off inside and part blocking it? could this cause it?

If i was to replace the CAT would i need to replace the o2 sensor or are they generally ok?

Last but not least is there away with checking the fault codes on mine (something to do with the dash milometer flashing etc?
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post #6 of 10 Old 01-16-2008, 10:39 AM
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IAC = idle air controller.. it sets idle speed.

it may be when the cats cold its blocked a bit but when it warms up it expands a little and unblocks a bit. but even if the cats not the problem if it rattles you need a new one anyway. not sure about reusing the o2 sensor.

pretty sure for a 98 you need an OBDII code reader.
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post #7 of 10 Old 01-16-2008, 11:14 AM
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had that problem.. put a new battery in and bang fires up great now!

had to rev the engine a bit on cold starts right from the turnover.. was not good.
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post #8 of 10 Old 01-16-2008, 06:20 PM
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Check your local dealer on the cat issue, they had a recall on certain years just for that problem, got the one on my 96 replaced for free.

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post #9 of 10 Old 01-18-2008, 01:05 AM Thread Starter
L20KEV
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Quote:
Originally Posted by rbright
Check your local dealer on the cat issue, they had a recall on certain years just for that problem, got the one on my 96 replaced for free.
does the recall have an expiry date? is there a list of what was recalled anywhere?

thanks
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post #10 of 10 Old 11-05-2011, 07:13 PM
autoposer
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Same solution

Quote:
Originally Posted by Mtb Jak View Post
had that problem.. put a new battery in and bang fires up great now!

had to rev the engine a bit on cold starts right from the turnover.. was not good.
My battery was only 12 months old, but was causing the same symptoms and once replaced fixed the issues. I tried cleaning the idle control valve and throttle body first. Even though it didn't fix the issue it now idles like it did 12 years ago despite have 170K miles on it. Highly recommend cleaning the IAC regardless.
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