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Its keeps getting to high

S

SINCITY192

NAXJA Forum User
Location
Bronx, NY
88 XJ 4.0 L 6cyl

Every time I start the jeep the idle is just too high man.
I am under the assumption that it might b cause by the idle crew on the TB
because I remember having to adjust it a long time back to keep the jeep driving (but that history) I just felt like it can but i dont think its a vac leak because i pay so much attention to my lines and what not.
I took a poke at it and turn the screw down some and the engine seems to idle way lower but in a good way, not tryna shut off!! so i should be in the clear!
Accelerating didn't seem to make the idle go high either.
(which that usually happens)
I will drive it to work and see how it feels with the idle tool ready incase i need adjustments.
any ideas?
if i shouldn't be messing with it let me know!
 
Base idle for the 4.0 is computer controlled.

Have you tried a thorough cleaning of both the IAC (idle air control) and the throttle body? They get carboned up over time and miles.

This would be a good place to start.
 
Sorry I forgot where I was posting on lol.
Basics I adjusted the idle adjustment screw, in hopes of fixing a
this high idle that just returned more meaner then ever.
i turned it down a notch or 2.
 
Have you checked the mating of the head to the intake manifold and exhaust manifold for leaks?

I seem to recall this coming up as something I would be suspicious of in your multitude of previous threads on this vehicle.
 
birchlakeXJ said:
Base idle for the 4.0 is computer controlled.

Have you tried a thorough cleaning of both the IAC (idle air control) and the throttle body? They get carboned up over time and miles.

This would be a good place to start.
Click to expand...

I starting to believe I clean these things to often! (IAC and TB)

after adjusting the little screw where (you can accelerate by hand on the linkage thing)
It started up high and went back down to normal
seriously before I adjusted this thing (u need the L shape tiny little allen key) the engine was idling as if I had my feet pressing the gas a little.
Now its so much smother to me!! But u know how things start out fine then mess up thats why im sharing
 
kastein said:
Have you checked the mating of the head to the intake manifold and exhaust manifold for leaks?

I seem to recall this coming up as something I would be suspicious of in your multitude of previous threads on this vehicle.
Click to expand...

Glad u mentioned that because when I was changing my mounts I made sure to put a torque wrench down there while I was there and tighten things up
alot seemed tight I was afraid to over tighten those but I did find 1 or 2 loosened bolts closest to the firewall (back of engine) where they meet and........ not a lot of space.. only could get my 1/2 inch smaller wrench in there but i figured since it was 1/2 it was still strong enough to do it.

and I didnt seem to be getting high idle any more but it kept tryna shut off on me (previous threads explain) I cured that by changing the Coolant temp sensor and Now the high idle is back... thats when I adjust the said screw above hope this sums it up.
 
Did you replace the gasket or just tighten it down? How many times has the head and the manifolds been off without replacing that gasket? You've gone through it a couple times and I don't recall if you ever did, nor if you scraped the head and manifold mating surfaces clean with a razor and brake cleaner before reassembling.

hasta hasta
 
kastein said:
Did you replace the gasket or just tighten it down? How many times has the head and the manifolds been off without replacing that gasket? You've gone through it a couple times and I don't recall if you ever did, nor if you scraped the head and manifold mating surfaces clean with a razor and brake cleaner before reassembling.

hasta hasta
Click to expand...

Wait only time I ever took the manifold off was when I change my head gasket and I did clean everything off took me three days 1 day of that was cleaning everything (but that was 1 1/2 or 2 yrs ago) I didnt think I had to replace the gasket so i just tightened
since I have to go to work I will let u know how it goes on the drive to work

Thanks everyone
 
Every high-idle episode that I have had on my 1990 4.0 Renix XJ has been from a dying TPS. Adjusting the idle screw just covers up the problem...... you need a properly-functioning TPS to manage the engine, and to manage the transmission shift points if you have the automatic AW4.
 
it is possible that since you adjusted the idle stop screw previously, it was out of adjustment. If you returned it to somewhere close to it's original position, you'd be getting closer to where it belongs---but remember that any time you move the throttle from it's original position, you've got to re-adjust the TPS to it's current location.
 
4xBob said:
Every high-idle episode that I have had on my 1990 4.0 Renix XJ has been from a dying TPS. Adjusting the idle screw just covers up the problem...... you need a properly-functioning TPS to manage the engine, and to manage the transmission shift points if you have the automatic AW4.
Click to expand...


Here's your answer, most likely....................
 
You're not supposed to mess with the stop screw. It's not a carburetor, that is not an idle adjustment point.

Why on earth would anybody think it was ok to reuse an old manifold gasket?
 
There is NO idle adjustment screw on the throttle body. Period.

There is, however, a small 3/32" allen screw, and its correct name is "The Little Screw That Keeps the Steel Throttle Plate from Slamming Closed Against the Alloy Throttle Body Wall and Causing Irreparable Harm".

Remove the intake. Turn the screw out so that it no longer touches or has any effect on the throttle plate. Now, carefully turn the screw back in--AT THE FIRST PERCEPTIBLE MOVEMENT OF THE THROTTLE PLATE, STOP TURNING THE SCREW--there, you have just set the throttle plate rest correctly. NOW LEAVE IT ALONE.

The ECU/PCM sends extend/retract commands to the IAC stepper motor to control the idle. If the idle isn't correct, clean the throttle body and IAC port, clean the pintle on the IAC--CAREFULL, it can break. Now, if the TPS is within specs and the idle is not correct--700~750 rpm (for an auto trans, check idle after 20 minutes of operation and while the vehicle is in DRIVE--have someone sit in driver's seat and hold the service brake pedal while testing), and you have checked for intake/vacuum leaks, then replace the IAC.
 
X2 - Especially setting the little allen screw like Joe says. That is the important place to start. That is where the screw HAS TO BE. I believe that the TPS then needs to be adjusted to THAT closed position.
 
Shorty said:
If you returned it to somewhere close to it's original position, you'd be getting closer to where it belongs---but remember that any time you move the throttle from it's original position, you've got to re-adjust the TPS to it's current location.
Click to expand...

winterbeater said:
X2 - Especially setting the little allen screw like Joe says. That is the important place to start. That is where the screw HAS TO BE. I believe that the TPS then needs to be adjusted to THAT closed position.
Click to expand...


I've heard all that before.... somewhere....
 
joe_peters said:
There is NO idle adjustment screw on the throttle body. Period.

There is, however, a small 3/32" allen screw, and its correct name is "The Little Screw That Keeps the Steel Throttle Plate from Slamming Closed Against the Alloy Throttle Body Wall and Causing Irreparable Harm".

Remove the intake. Turn the screw out so that it no longer touches or has any effect on the throttle plate. Now, carefully turn the screw back in--AT THE FIRST PERCEPTIBLE MOVEMENT OF THE THROTTLE PLATE, STOP TURNING THE SCREW--there, you have just set the throttle plate rest correctly. NOW LEAVE IT ALONE.
Click to expand...

I am assuming I must do this with jeep off. (because with jeep running turning that screw makes the idle go up as I push the plate further away but as I bring the same plate closer but not touching the idle of the car just seemed better) (can anyone explain that?)

now for removing the intake, do you mean the hoses or the whole intake manifold.(call me careful because i jus wanna be sure)

as for the point where your telling me to set it., if i understand it correctly the concept is to just have it so the plate does touch the Alloy.
so it coming out just a bit is good right?
 
joe_peters said:
There is NO idle adjustment screw on the throttle body. Period.

There is, however, a small 3/32" allen screw, and its correct name is "The Little Screw That Keeps the Steel Throttle Plate from Slamming Closed Against the Alloy Throttle Body Wall and Causing Irreparable Harm".

Remove the intake. Turn the screw out so that it no longer touches or has any effect on the throttle plate. Now, carefully turn the screw back in--AT THE FIRST PERCEPTIBLE MOVEMENT OF THE THROTTLE PLATE, STOP TURNING THE SCREW--there, you have just set the throttle plate rest correctly. NOW LEAVE IT ALONE.

The ECU/PCM sends extend/retract commands to the IAC stepper motor to control the idle. If the idle isn't correct, clean the throttle body and IAC port, clean the pintle on the IAC--CAREFULL, it can break. Now, if the TPS is within specs and the idle is not correct--700~750 rpm (for an auto trans, check idle after 20 minutes of operation and while the vehicle is in DRIVE--have someone sit in driver's seat and hold the service brake pedal while testing), and you have checked for intake/vacuum leaks, then replace the IAC.
Click to expand...

SINCITY192 said:
I am assuming I must do this with jeep off. (because with jeep running turning that screw makes the idle go up as I push the plate further away but as I bring the same plate closer but not touching the idle of the car just seemed better) (can anyone explain that?)

now for removing the intake, do you mean the hoses or the whole intake manifold.(call me careful because i jus wanna be sure)

as for the point where your telling me to set it., if i understand it correctly the concept is to just have it so the plate does touch the Alloy.
so it coming out just a bit is good right?
Click to expand...


:twak: It's official, all nominations past this point are null and void.
 
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