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  #1  
Old August 11th, 2020, 09:58
efjellanger efjellanger is offline
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Throttle hanging

Hi all, this is the first thread I've posted here. I am a new owner of a 1998 XJ, with about 200k miles but a nearly new engine. It's been fun, and since it's a 22 year old vehicle, there's enough slightly wrong with it to keep me occupied.


It has experienced a high idle intermittently since I bought it. If I snap the accelerator briskly it'll settle down. This is my first XJ so I don't have any other comparison, I would say the idle seems just a little rough right now, but it might be normal.


I have taken the throttle body off a couple times, cleaned it, fiddled with the stop screw, then I replaced the gasket and eventually replaced the IAC valve and the housing gasket. None of these have really made the problem go away.



So finally in desperation I actually looked at the throttle while it was experiencing the high idle. The throttle actuator is not sitting on the stop screw. If I push on it, I can get it to seat down and it goes back to a normal idle. During this, all 3 cables (accel, cruise, TV) going to the actuator are loose.



So I can't tell why it's hanging, but it seems to be internal. What do I need to fix this? Clean it out again, better? Disassemble and sand it? A new throttle body?


Probably unrelated bonus problems: a few times I have had a low voltage at idle which resulted in a "Check gauges" light. Seemed more common with the headlights and fan on. I haven't seen it again since the first time I cleaned the TB. I also had a missing vacuum line going to the reservoir, I replaced that and the dash vents started working, which was great. The idle seemed to smooth a bit after that.



thanks in advance,
E
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  #2  
Old August 11th, 2020, 15:55
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Tim_MN Tim_MN is offline
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Re: Throttle hanging

If the Idle Air Controller (IAC) is not a genuine Jeep part, it is suspect. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Cheap parts are cheap for a reason.

It is possible that the throttle body is worn. but the IAC controls the idle so you should not mess with the mechanical stop screw. I have a couple spare TB's in the garage and I don't think any of them mechanically close completely. If the TB butterfly closes properly with the TPS removed, the TB should be good. My 1998 has +284,000 miles and the original TB. The IAC was replaced when the idle would either stall the motor, or randomly flare to a high idle.

Read this >> https://www.naxja.org/forum/showthread.php?t=1158252
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Last edited by Tim_MN; August 12th, 2020 at 10:35.
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  #3  
Old August 11th, 2020, 17:55
Agreen Agreen is offline
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Re: Throttle hanging

If you unplug the IAC does the idle go down? If no, I'd spray a little penetrating oil on the throttle shaft to see if it no longer gets hung up. If that solves it, it won't for long. Penetrating oil isn't a lubricant (contrary to what some believe). Your best bet is either a new or junkyard TB.

The low voltage is most likely battery cable ends. Mine were so corroded I had to replace the whole cable. I couldn't strip the cable back far enough to NOT get green copper strands. I don't remember the exact sizes, but I took the cables out and measured them up. Yes, you have to carefully cut the harness loom, but it's not hard when you remove the battery and battery tray. Use the marine style terminals that have wingnuts so you can put ring lug ended cables on. Everything I used set me back about $40.
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  #4  
Old August 11th, 2020, 18:18
lawsoncl lawsoncl is offline
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Re: Throttle hanging

Yeah, don't muck with the throttle stop screw. I'm not sure if the gap on the HO engines is the same as the Renix, but here is the procedure for resetting it - http://cruiser54.com/?p=94.
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  #5  
Old August 12th, 2020, 08:54
efjellanger efjellanger is offline
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Re: Throttle hanging

I meant to say up front that IAC is a real Mopar part. I understand the IAC controls the idle, but it is only able to do so if the TB closes properly, right?



I'll try penetrating oil on the throttle shaft. This is not possible to lube?



I'll check the battery cables. My battery tray is (predictably?) also toast so it'll be good to take care of that too. I think there's a fair amount of corrosion there so I'll prepare for a headache.
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  #6  
Old August 12th, 2020, 09:08
RCP Phx RCP Phx is offline
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Re: Throttle hanging

I have had problems in the past with binding from the TPS.
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  #7  
Old August 12th, 2020, 11:17
Agreen Agreen is offline
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Re: Throttle hanging

The IAC will get a signal from the ECU to raise or lower idle speed by allowing more or less air to bypass the throttle. If the throttle is stuck partially open and the ECU is commanding a lower rpm, the IAC can't make any change in idle speed.

I don't remember if you can pull the throttle shaft out or not. You might be able to pull the screws from the butterfly and shaft, slide the shaft out and add a little graphite lube in there.

Try what RCP said. Just remove the TPS and see if it goes shut more. If so, snag a new TPS.
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  #8  
Old August 12th, 2020, 20:47
jk_surgeonfish jk_surgeonfish is offline
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Re: Throttle hanging

Mine did this. It was the butterfly valve making just a bit of contact on the TB itself when closing. It would idle high until as you described snapped the throttle and it settled down. The bushing in the butterfly valve in the TB was warn causing it not to close smoothly. I ended up getting a new TB and it solved the issue. You can manually open and close it and will be able to feel resistance when it is almost closed.
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Old August 12th, 2020, 20:48
jk_surgeonfish jk_surgeonfish is offline
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Re: Throttle hanging

Quote:
Originally Posted by jk_surgeonfish View Post
Mine did this. It was the butterfly valve making just a bit of contact on the TB itself when closing. It would idle high until as you described snapped the throttle and it settled down. The bushing in the butterfly valve in the TB was warn causing it not to close smoothly. I ended up getting a new TB and it solved the issue. You can manually open and close it and will be able to feel resistance when it is almost closed.



When I say new.. it was from the junkyard and I swapped all sensors from mine to the donor TB.
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Old August 13th, 2020, 07:54
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8Mud 8Mud is offline
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Re: Throttle hanging

The first thing I'd look at is the carpet and padding, it has been known to hang up the pedal, look close with a flashlight, get your, eyeball right up next to the bottom of the pedal and look around the back. On my old Renix mine would occasionally stick, I looked but didn't really see, I eventually spotted the problem after a close examination. The second thing is the throttl return spring, a broken clock spring can be hard to spot the break/crack almost invisible. The third thing is both the TV cable and throttle cable, unhook them and try them by hand to see if they have a sticky spot or they are maybe frayed under the cable shell. Work the throottle by hand slowely and feel for sticking. It only takes one broken cable strand to mess up reliabilty.

A good lubricant for spots like that (throttle plate rod) is a good Moly motorcacle chain lube, It doesn't run and is high temp resistant. Just a drop or two will do you, I've been using the same spray can for decades and it is still half full, also works well on hinges. Spray the old lubricant out with brake cleaner and then apply the Moly Lube.
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  #11  
Old August 18th, 2020, 09:13
efjellanger efjellanger is offline
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Re: Throttle hanging

Well it's treated me to a couple completely different symptoms over the last week:


1. After a cool start, the idle went up to near 2k, then after a few moments dropped down to about 500 and started hunting back and forth from 500-1000. I stepped on the gas after a bit to try and smooth it out, and the idle went back to near 2k. It wouldn't settle down after this, and I drove home a half hour, when I got there it was still idling high.


2. My wife drove it and when she brought it home said it was showing the "check gauge" light. I tried to start it and the battery had died, so I jumped it. When started it was idling appropriately, but the voltage was low and the check gauges light was on.


#2 seems like some intermittent short. Is there a relay that could explain this? Or some cables I should particularly suspect?


I have a new TPS in the mail. Starting to see some reasons the PO might have wanted to sell this rig right after replacing the engine.
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Old August 18th, 2020, 14:00
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Re: Throttle hanging

A bad battery re-boots the PCM and deletes the idle settings. A bad alternator results in low battery voltage, and a re-booted PCM with no idle settings. If the symptoms persist with a good alternator and battery, clean and snug alternator and battery cables, clean and snug grounds, I would suspect the IAC.

Around here, a good used TB is $22 with the sensors still attached.
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Quote:
Originally Posted by bimmerjeeper


Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
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  #13  
Old August 18th, 2020, 14:27
efjellanger efjellanger is offline
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Re: Throttle hanging

The battery is new, unfortunately it's been drained a few times now. The alternator may be suspect, how do I check it? If I could buy a TB for $22 that wouldn't be a tough decision to try it.

My feeling is that it's draining just sitting still and turned off though. She didn't drive it very far, and by the time I tried the battery could barely turn the engine over and couldn't start it.
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Old August 18th, 2020, 19:09
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old_man old_man is offline
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Re: Throttle hanging

You do still have the throttle return spring...right. Some models even have two.
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  #15  
Old August 19th, 2020, 09:39
efjellanger efjellanger is offline
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Re: Throttle hanging

Yes, mine has just the coil spring wound around the throttle shaft. I wondered if a secondary spring was missing, but I've now seen I can have a bad idle with the throttle completely closed. So this seems like at least a couple overlapping intermittent problems.
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