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Unread 05-12-2012, 06:42 PM   #1
APEDZ04LJ
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04 lj rough/low idle in drive

ok so 04 lj, im geting a intermitent rough/low idle at a stop in drive, goes down to the first dot on the tach, already cleaned the iac, had autolite 985s in it, im gonna try ngks tomorow, i read a bad tps? or fuel pressure? how can i test fuel pressure?

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Unread 05-12-2012, 06:48 PM   #2
Jerry Bransford
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Probably a sticky/dirty IAC (idle air control) which is what provides all of the engine's air at idle when you're not stepping on the accelerator pedal. The IAC is a solenoid actuated plunger that moves in and out of an oriface in the throttle body to provide the engine's air at idle. The IAC's plunger and the oriface (hole) in the throttle body can be cleaned with throttle body cleaner and restored back to good operation.
tb-tps-sensor-locations.jpg  
iac.jpg

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Unread 05-12-2012, 07:02 PM   #3
APEDZ04LJ
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Quote:
Originally Posted by Jerry Bransford View Post
Probably a sticky/dirty IAC (idle air control) which is what provides all of the engine's air at idle when you're not stepping on the accelerator pedal. The IAC is a solenoid actuated plunger that moves in and out of an oriface in the throttle body to provide the engine's air at idle. The IAC's plunger and the oriface (hole) in the throttle body can be cleaned with throttle body cleaner and restored back to good operation.
i already pulled the i ac and the tb apart and cleaned it all out, it wasent that dirty, still have the problem
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Unread 05-12-2012, 07:14 PM   #4
APEDZ04LJ
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these are the plugs i had in it http://www.autozone.com/autozone/par...er=105742_0_0_
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Unread 05-12-2012, 11:14 PM   #5
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Quote:
Originally Posted by APEDZ04LJ View Post
i already pulled the i ac and the tb apart and cleaned it all out, it wasent that dirty, still have the problem
Can you define "wasn't that dirty" and describe how you cleaned it?

I will tell you this-I can't count the number of rigs I've cured this issue on after folks have told me the exact same thing...

To clean properly, you MUST remove everything, and scrub every nook and cranny with a tooth brush thoroughly using a good TB cleaner. Exercise the plunger on the IAC and scrub it too, along with opening the throttle plate and removing the haze around the ring. You want a mirror finish here on all of it-if you don't have that, it isn't clean enough. Absolutely no haze or dark color of any kind-if you have that, it isn't clean enough and it will lead to rough idle and surge conditions. Sorry, not that I don't trust your cleaning job, but I've been told that more times than I can count and it wasn't clean enough which lead to the same issues you have here.

How many miles on the rig and is it totally stock? You don't have one of those screwy jet chips or anything like that do you? No TB spacers or other gimmicks?

Stick with factory plugs as well-regular NGKs are hard to beat.

Best of Luck,

Mike
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Unread 05-18-2012, 12:20 PM   #6
APEDZ04LJ
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Ok so i tried new plugs, and a new iac and that didnt solve it
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Unread 05-18-2012, 06:58 PM   #7
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bump for an anwser on what i should look at next
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Unread 05-18-2012, 07:02 PM   #8
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Any codes from the computer? I had a cylinder not firing due to my ignition rail pack on the #4 cylinder going bad.
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Unread 05-18-2012, 07:29 PM   #9
APEDZ04LJ
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Nope no codes
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Unread 07-24-2012, 06:55 PM   #10
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bumping for update, ive sprayed all vaccum lines and nothing changed rpm wise, ive tryed another throttle body with all different sensors, it still surges at idle but now at start up it revs up to 1800 then idles at 1100, it also know surges while cruising only for a certain gear, i have no clue whats going on here and no codes at all
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