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Discussion Starter · #1 ·
I bought a 98 Wrangler SE 2 weeks ago. Its a Manual Trans. On most of the start ups it cranks up around 1500 rpm then quickly drops to 700ish, whether the engine is hot or cold. However, on some start ups it will crank and then sit around 2,000 rpm and stay there. The first time it happened I just drove it around and after a few stop lights it started to come back down to normal levels. I have also found that if I start it and it does the 2k rpm thing I can cut it off and start back up and it usually gets back to the 700 rpm range on the 2nd start up.

Any idea what could be causing this? Has anyone else had this issue?
 

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Did you try cleaning the throttle body and IAC? Just be sure not to use carb cleaner to clean the throttle body. You might also want to check the TPS as well. Vacuum leaks can also cause idle problems, but I don't think that's the case here, still worth checking though.
 

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Discussion Starter · #3 ·
Did you try cleaning the throttle body and IAC? Just be sure not to use carb cleaner to clean the throttle body. You might also want to check the TPS as well. Vacuum leaks can also cause idle problems, but I don't think that's the case here, still worth checking though.
I haven't yet but after posting this I did some more checking around and I will certainly start with the cleaning of all the parts around the TB and IAC. Certainly can't hurt to clean those parts even if it doesn't fix the issue.
 

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Discussion Starter · #4 ·
Over the weekend I removed and cleaned the throttle body and IAC really well and also changed the air filter that was unbelievably dirty (kicking myself in the arse for not looking at it sooner). It starts up quicker, returns to 600-800 rpms quicker, runs a 100 times better and accelerates more smoothly since cleaning these parts. The high idle issue happened about 1 of ever 15-20 start ups, I have started it probably 20 times without even a hint of an issue. I hope this solved my problems. I will update in a few days after I get some more start ups in.
 

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I know what this is!!!!! I had this problem with my 98 wrangler. It is the idle control is broken. People will tell you its the intake and vacuum seals but I would bet its the Idle control. Got mine fixed after I couldn't figure it out. Shop can do it for like 150. Was happening to me, Starts up sits around 2k and then comes back down after like 15 minutes. It's the idle control.
 

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Discussion Starter · #7 ·
I cleaned the throttle body and Idle Air Control and so far it hasn't messed up again. If it acts up again I will replace the Idle Air Control. I won't pay a shop to do it though. The part is $41 and its only held in place by 2 screws.. $150 at the shop seems WAY HIGH..
 

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Did you try cleaning the throttle body and IAC? Just be sure not to use carb cleaner to clean the throttle body. You might also want to check the TPS as well. Vacuum leaks can also cause idle problems, but I don't think that's the case here, still worth checking though.
I have these issues and I used carb cleaner when cleaning my tb, my issues still persist. Why do you say not to use carb cleaner? Have I been destroying ny engine?
 

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For purposes of what you're doing, carb and throttle body cleaners are essentially the same thing. If it says "sensor safe" on the can as all I have seen in recent years have said, it's fine.
 

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Thank you Jerry.

NC Rick I am glad to hear your problems were resolved. I am baffled however how the IAC replacement has done nothing for me yet cured so many others with a High Idle. I am going to remove the IAC, replace with the older one, and attempt to get my $ back.

But none the less I am still stuck at square one. sigh.
 

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Stores will seldom refund the $$$ for electrical devices like the IAC. My bet is you have a vacuum leak which will cause high RPMs.
 

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I have these issues and I used carb cleaner when cleaning my tb, my issues still persist. Why do you say not to use carb cleaner? Have I been destroying ny engine?

In some instances carb cleaner can destroy a coating on the throttle plate. Which is why many people use throttle body cleaner instead.

Have you checked for vacuum leaks and if the IAC is clean? They get fouled and every once in a while you can get lucky cleaning one. There are also ways to test the IAC, Google it for your application. I have a feeling your IAC is bad. Try and make friends with someone at a parts store, they might allow you to return it if it isn't the offending part, and you can't test yours for some reason.
 

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What coating would that be? There's nothing in my throttle body or its throttle valve plate that has any kind of coating on it.
 

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What coating would that be? There's nothing in my throttle body or its throttle valve plate that has any kind of coating on it.

Some mfgs. used a coating similar to a Teflon coating making it a bit harder for carbon to attach itself to the throttle body plate. Ford used a coating on theirs at some point and might still use it, and went on to say in some of their shop manuals: "CAUTION: The throttle body bore and plate area have a special coating and cannot be cleaned."

Then there are throttle body cleaners that say they're safe to use on coated throttle bodies. CRC Throttle Body & Air Intake Cleaner, says "Safe for use on coated throttle bodies." Since I have no idea what vehicles used coated throttle bodies I use throttle body cleaner and play it safe. Opinions vary.
 
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