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Old February 22nd, 2006, 04:11 PM   #1
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Default since i cant figure this out, you can try

problem: 1990 xj 4.0L 100K (runs strong) aw4 np242

start up it will idle normal ~700rpm

after about 4 minutes of just idle the rpm's will slowly increase to 1000 then to about 1200.. at this time the engine temp is about 160 degrees

ill take it for a short drive and come back put it in park and the idle will be at 1500 to 1700rpm. temp will be normal at 190

i can't get the idle down <------------------------------

* what i did so far to try to fix:
1. replaced TPS
2. new plugs, rotor, cap
3.. tested ohms and volts of the intake air temp sensor, MAP, Coolent temp sensor
4. cleaned the throttle boddy (took it all apart cleaned iac motor..yadda)
5. checked for any vac leaks with propane

this year does not have a check engine light, so i cant check any codes?




have not checked the O2 sensor yet but has been replaced aproxx 40K ago


hank you very freaking much if someone can help me
alan
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Old February 22nd, 2006, 06:49 PM   #2
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if I had to guess I would look at the coolant sensors themselves. its acting like it may be trying to give fast idle because it doesn't know the engine is warm. is it running rich? if so then It deffinatly points to coolant sensors.
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Old February 22nd, 2006, 08:23 PM   #3
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Do you have an "Idle air controller" on that? How about an EGR valve.....that's where I'd start from where you left off.
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Old February 22nd, 2006, 08:37 PM   #4
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The PCV valve on my Cavalier caused it to idle somewhere close to 2K. But that was a special instance where there basically was no valve.. long story, don't want to hi-jack. Cheap and easy to replace too.
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Old February 22nd, 2006, 08:49 PM   #5
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check for vac leaks also, they can cause strange idle issues.
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Old February 23rd, 2006, 04:43 PM   #6
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thanks so far for the responses.

yes it does have an idle air controller, checked that and found not to be the problem,

i took it to a shop in livonia (5 mile and levan) to tell me whats wrong, to make a long story short they told me i needed to replace the TPS (that i already rteplaced before hand) they wanted 149 for the part, .6 hours to install it, $12 for shop rags and $3 for a screw to hold the TPS and $80 to tell me whats wrong

for a total of $305.70 :miff:

i didnt pay anything and they told me never to come back

$69 for the TPS at autozone and it took me 10 minutes to replace it

Last edited by xjmichigan; February 23rd, 2006 at 04:45 PM.
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Old February 23rd, 2006, 04:46 PM   #7
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yetti: ill replace the CTS, like you said,

anyone else? have any ideas


alan
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Old February 23rd, 2006, 05:26 PM   #8
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My 02 sensor was bad and my idle bounced around (up and down 800-1,500rpm) hope this helps ?
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Old February 23rd, 2006, 08:21 PM   #9
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Quote:
Originally Posted by One Arm Steve
My 02 sensor was bad and my idle bounced around (up and down 800-1,500rpm) hope this helps ?

really, well i guess mine could go bad in such a short time, ill replace that too and let you know

thanks
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Old February 24th, 2006, 05:26 PM   #10
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heres what happened so far:

if i cool off the 02 sensor after it is warmed up with a spray of water the idle returns to normal (700)

i guess the o2 must be the problem, auto place didnt have one in stock today

have you ever heard of cooling off the senor like that?!?!
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Old February 24th, 2006, 05:31 PM   #11
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the only thing I can think of is if the O2 sensor is causing a surge in idle speed it could be its a preheated (4 wire) sensor and the heating elemnt could be shorted out. I have never heard of sensor doing that before.
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Old February 24th, 2006, 08:01 PM   #12
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My 90 XJ did the same exact thing, replaced all sorts of $hit. Sold it to a guy at work, still had idle problem. It turned out to be the connection of vacuum and breather lines on the drivers side up by the radiator.
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Old February 28th, 2006, 05:59 PM   #13
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Default ***update***

thanks for all who helped...

i bet you want to know what was really wrong...

it was the #3, 4, 5 intake port were sucking in small amounts of air through the intake gasket.

i tightened all intake and exhaust bolts and it seems to be problem solved
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