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Author Topic: weird idle problem  (Read 2740 times)

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tallrugbyguy

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weird idle problem
« on: December 01, 2008, 10:19:17 PM »
so my jeep idles really low. not sure if that is a bad thing about 700rpm.

but the problem is is when i start my jeep, the the engine will trun over then stop right away. if i give a bit of gas then she struggles through and after i rev it up its totally fine. seems to happen on cold starts.

i did just put a 62mm tb on. but i think this happened once before that conversion.
any ideas? i know my computer is shot and im still waiting for a new one. can that be it?
« Last Edit: December 01, 2008, 10:26:29 PM by tallrugbyguy »
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Offline Jeffy

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Re: weird idle problem
« Reply #1 on: December 02, 2008, 12:03:34 AM »
Quote from: tallrugbyguy on December 01, 2008, 10:19:17 PM
so my jeep idles really low. not sure if that is a bad thing about 700rpm.

but the problem is is when i start my jeep, the the engine will trun over then stop right away. if i give a bit of gas then she struggles through and after i rev it up its totally fine. seems to happen on cold starts.

i did just put a 62mm tb on. but i think this happened once before that conversion.
any ideas? i know my computer is shot and im still waiting for a new one. can that be it?

700RPM is the normal RPM at idle.  Actually I think it's 750RPM.  If this is new, then I'd swap back to the stock TB and see if it is, just to be sure.  The only other thing I can think if is the TPS might not be working right.  Also make sure you have all of the vacuum lines connected.
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"If the motor car were invented today, there is absolutely no way that any government in the world would let normal members of the public drive one."

Tsd

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Re: weird idle problem
« Reply #2 on: December 02, 2008, 05:39:18 AM »
May be one of the TB sensors was not fully reconnected after the TB swap?  :confused:
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TrailsLessTaken

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Re: weird idle problem
« Reply #3 on: December 02, 2008, 06:58:54 AM »
Mine started doing that too right after I did the injectors, throttle body and PD kit, and I think its just the computer hasnt adjusted yet, cause if i keep the rpm's up for about 30 seconds and let the engine warm up some and the computer can start adjusting then its fine after that
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tallrugbyguy

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Re: weird idle problem
« Reply #4 on: December 02, 2008, 09:54:51 AM »
long did that happen to you for?
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TrailsLessTaken

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Re: weird idle problem
« Reply #5 on: December 02, 2008, 10:22:28 AM »
Its still doing it, I just put them on this summer and have only put i think 125 miles on the jeep since I did all that.  I can hear when it starts up that its sucking in a ton of air and it seems like once it gets the fuel mixture worked out then it quits running rough and drops down to about 6-700 i think maybe a lil higher I cant remember
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Offline Jeffy

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Re: weird idle problem
« Reply #6 on: December 02, 2008, 11:27:58 AM »
Quote from: TrailsLessTaken on December 02, 2008, 10:22:28 AM
Its still doing it, I just put them on this summer and have only put i think 125 miles on the jeep since I did all that.  I can hear when it starts up that its sucking in a ton of air and it seems like once it gets the fuel mixture worked out then it quits running rough and drops down to about 6-700 i think maybe a lil higher I cant remember

A vacuum leak will cause the idle to be high.  Also, installing a 2.5L IAS sensor in a 4.0L IAS housing will cause a leak as well.  Idle usually jumps to 1000RPM.
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"If the motor car were invented today, there is absolutely no way that any government in the world would let normal members of the public drive one."

TrailsLessTaken

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Re: weird idle problem
« Reply #7 on: December 02, 2008, 11:52:43 AM »
Yeah but wouldn't the motor do that everytime it starts up Jeffy? Mine only does it the first time and then once its warmed up, if I stall it on the trail or something when I restart, it doesnt do that again. 
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Offline lax22

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Re: weird idle problem
« Reply #8 on: December 02, 2008, 07:31:06 PM »
I did my 4.0TB swap this past summer and i have a weird idle as well. With the stock TB and TBS it idled smooth and steady at 700rpm. I took off the TBS and the 2.5l TB and as soon as the new 4.0l TB went on the RPMs jump up and down between 700 and 800 rpm at idle. I have replaced the TB gasket and even checked the 2.5l IAC housing and everything is sealed and tight. I would like to fix it without switching back but its starting to get annoying. I have a new TPS and IAC. The only thing i can think is that the engine is getting too much air if that even makes any sense since i am running the 4.0l intake tube with an arrait intake. Any suggestions? I would assume that the computer would have readjusted by now.
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Offline chardrc

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Re: weird idle problem
« Reply #9 on: December 02, 2008, 08:57:13 PM »
don't they create a vacuum leak when the berring / shaft assembly for the tb "butterfly vavle" :confused:goes bad,
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Offline Jeffy

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Re: weird idle problem
« Reply #10 on: December 02, 2008, 09:27:19 PM »
Quote from: TrailsLessTaken on December 02, 2008, 11:52:43 AM
Yeah but wouldn't the motor do that everytime it starts up Jeffy? Mine only does it the first time and then once its warmed up, if I stall it on the trail or something when I restart, it doesnt do that again. 

Normally, yes.  Although I'm wondering if it's the IAC.  The IAC acts like a choke when cold, IIRC.  I believe once the engine's up to temp, it no longer is used.
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"If the motor car were invented today, there is absolutely no way that any government in the world would let normal members of the public drive one."

TrailsLessTaken

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Re: weird idle problem
« Reply #11 on: December 02, 2008, 09:56:03 PM »
I replaced mine with a brand new IAC and TPS when I did the swap, so unless it was bad to begin with...
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Offline lax22

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Re: weird idle problem
« Reply #12 on: December 03, 2008, 05:33:57 AM »
Quote from: TrailsLessTaken on December 02, 2008, 09:56:03 PM
I replaced mine with a brand new IAC and TPS when I did the swap, so unless it was bad to begin with...

I did the same and still not a smooth idle. I might try and put the old setuo back on and see if that dose anything. Maybe adjust the screw on the throttle body, I dont know.
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TrailsLessTaken

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Re: weird idle problem
« Reply #13 on: December 03, 2008, 06:23:45 AM »
Does yours do it constantly or just at startup then goes to just a normal idle
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Offline lax22

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Re: weird idle problem
« Reply #14 on: December 03, 2008, 08:18:02 AM »
At start up its around 900 it will settle down to 750 after warm up and then at idle fluxuates between 700 to 750 and 800. Its constant and only stops when the engine is inder an electrical load, ie elctric fan kicking on.
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