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Author Topic: 98 4l sport cherokee erratic idle  (Read 2061 times)

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BOP

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98 4l sport cherokee erratic idle
« on: March 17, 2010, 01:22:23 PM »

Needing some help here! my 98 cherokee is refusing to idle, if I have to stop at traffic lights, junctions etc it hunts up and down from about 100rpm up to 900rpm and will not settle, if its left to hunt up and down it cuts out after about 30 seconds to a minute and is then very hard to re-start, if it starts hunting and I put it into neutral or park and put handbrake on it'll raise the revs to just over 1000rpm and although still slightly hunting nowhere near as bad maybe only 50rpm if anything, but as soon as I put it back into drive and let handbrake off the revs drop straight away and it dies, if I pull off after it hunts as soon as I touch the throttle pedal it goes to die then clears and pulls away, it pulls fine everywhere else in the range and normal driving is fine, but as soon as I take foot off the go pedal revs drop and it goes to die! It does this 8 times out of 10 so its slightly intermittant but is getting worse! in the last 3-4 months I've changed the CPS,TPS,o2 sensor,spark plugs,H/T leads,air filter, it had a new dizzy on it a few months before I bought it last october, I've cleaned and checked the earths in the engine bay, I've stripped and cleaned the throttle body and cleaned the IAC but to no avail, the only thing I did notice when I stripped the throttle body is that the butterfly does'nt seal in the throttle body fully if you hold it up to the light you can see a small amount of light around circumference of the butterfly! anybody got any ideas on whats causing this as I'm stumped,and slightly pissed off as I have'nt been able to use it for last couple of months :icon_sad:
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Panic mechanic!

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Re: 98 4l sport cherokee erratic idle
« Reply #1 on: March 17, 2010, 03:05:09 PM »

Induction side air leak.
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Bulldog67

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Re: 98 4l sport cherokee erratic idle
« Reply #2 on: March 17, 2010, 06:14:57 PM »

no idea BOP but u have my sympathy, ya truck looked a great buy but the fucker has played up bad on ya :jpshakehead:
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grayspeed

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Re: 98 4l sport cherokee erratic idle
« Reply #3 on: March 17, 2010, 06:20:26 PM »

ECU temperature switch, 99%. Ask Green Jeep, it sorted his out after suffering the same symptoms.
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BOP

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Re: 98 4l sport cherokee erratic idle
« Reply #4 on: March 17, 2010, 08:19:15 PM »

no idea BOP but u have my sympathy, ya truck looked a great buy but the fucker has played up bad on ya :jpshakehead:

Cheers bulldog sometimes shit happens and I've just had steaming great piles of bad luck so far! Had it for 5 months and its only worked for a month an a half :010:
grayspeed is that the manifold air temperature switch? I've done the resistance tests on that one and it checks out ok! I'll have another look at back of block tommorrow and see if I can see another switch, do you know what its called if its not the manifold air temperature? I read about the one green jeep changed but aint been able to find it yet, could do with knowing what its called so i can look up where it is? the cam position sensor has been under suspicion of playing silly buggers but kinda need to narrow it down to which sensor it is before I spank another £60-150 quid on another sensor, I found out in january I'm about to become a dad later on this year so moneys gettin tight and electrical jiggery pokery for the buggy is not going down well :jpshakehead: but its a great lookin ornament parked outside the house :greggmo:
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isle of man

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Re: 98 4l sport cherokee erratic idle
« Reply #5 on: March 17, 2010, 08:42:22 PM »

Can you borrow another TPS from someone? your symptom has the perfect description for this.
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BOP

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Re: 98 4l sport cherokee erratic idle
« Reply #6 on: March 17, 2010, 09:02:10 PM »

Can you borrow another TPS from someone? your symptom has the perfect description for this.

yeah I've read and re-read posts regarding TPS issues wondering whether maybe the new one I bought was a duff one, I changed the TPS hoping to cure another electrical problem I had with it before christmas which turned out to be cps, I still have the original one in the garage so maybe worth plugging it in and trying it?
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isle of man

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Re: 98 4l sport cherokee erratic idle
« Reply #7 on: March 17, 2010, 09:05:29 PM »

Check for dirty/broken connections and wires at the same time - would be the logical route.
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greggmo

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Re: 98 4l sport cherokee erratic idle
« Reply #8 on: March 17, 2010, 11:01:22 PM »

ya all ready know i was thinkin cam sensor cos we spoke about it. i think the problem that we have is that we just aint landed on the one that is the problem. the original fault still exists the other new parts have just improved the rest of the stuff surrounding the problem. mick o had some stuff like this with his xj and it was the cam sensor. keep em comin guys we gotta get to the bottom of this before bop goes madder than he already is.
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BOP

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Re: 98 4l sport cherokee erratic idle
« Reply #9 on: March 18, 2010, 07:32:28 AM »

I'm willing to try anything!(steady!) most annoying thing is yesterday started it up again an it ran fine! grrrrrrr :017:
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Green Jeep

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Re: 98 4l sport cherokee erratic idle
« Reply #10 on: March 18, 2010, 10:09:51 PM »

ECU temperature switch, 99%. Ask Green Jeep, it sorted his out after suffering the same symptoms.

Yeah defo had same troubles, after changing many things from a breaker (ECU TPS, etc.... it came down to a tiny sensor at the back of the head, grayspeed hit the nail on the head, I changed the sensor and now normal rancho relaxo jeep serice has been resumed, happy days
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BOP

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Re: 98 4l sport cherokee erratic idle
« Reply #11 on: March 19, 2010, 07:34:50 AM »

I'll have another look for this switch later, tested the coolant temperature sensor yesterday and that checked out ok, does anybody know what sort of resistance/how to check the mat sensor as well? I'm just working my way through all the sensors at the moment with the volt meter to try and find whats going on!
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Green Jeep

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Re: 98 4l sport cherokee erratic idle
« Reply #12 on: March 19, 2010, 06:44:39 PM »

I'll have another look for this switch later, tested the coolant temperature sensor yesterday and that checked out ok, does anybody know what sort of resistance/how to check the mat sensor as well? I'm just working my way through all the sensors at the moment with the volt meter to try and find whats going on!

No, but I would guess it was cheap as chips for new sensor, top tip the plastic part pulls out and makes it easier to get a 13mm socket on, it's located right at the back of the head on the passenger side (assuming its a RHD) just has one wire going to it... I was lucky I had a second hand cly head with spare one in it... hope this helps, Maf
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prophet

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Re: 98 4l sport cherokee erratic idle
« Reply #13 on: March 19, 2010, 06:59:18 PM »

My 97 cherokee (4.0L) had a rough idle, it'd chug between 300 and 1000rpm. It never cut out, but felt close to it. All of these problems went away when I changed the upstream o2 sensor. It runs a lot sweeter now and uses half the fuel.

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