Really low idle and vibration

Hammer24

Hammer24

TJ Enthusiast
Joined
Jan 29, 2019
Messages
428
Location
Melbourne, Australia
So I'm having what I hope are a couple of minor issues with the Jeep at the moment. 2000 Sport, 4.0l manual. Over the last week, at about 100kmh she vibrates a little (not every time at 100 though weirdly), didn't think much of this however but started her up this morning and she was idling super low (around 200-300? although hard to tell off the analog guage) and vibrating quite a bit that the dash was shaking a little. It would sort of vibrate for 10 seconds and then the rpm would go up to about 400 (still low) for about 10 seconds, and then back down and then up etc,. Once i gave it some throttle and it warmed up it drove completely fine the whole hour home (except some those slight vibes at 100kmh that I mentioned). Not sure if the two issues are actually linked but it would be a weird coincidence if they weren't. Anyone have any ideas?

Cheers
 
Your high-speed vibration is most likely unbalanced tires. As for the low idle, I'd clean out the idle air controller, which is often the culprit for rough idles.
 
Yes and check for vacuum leaks and remember you can occasionally get bad fuel especially if there's a lot of rain in your area.

A set of correctly gapped spark plugs would also be a good idea at that mileage point if they have not been replaced in a while.

Read some threads and be sure you get the correct ones.
 
Pretty much all engines will give you a vibe at 200 rpm. So don't worry about that part. Did this happen just the once? The super low idle I mean. It could be a fluke, a speck of water in the gas, a bad tank of gas, etc. If it turns into a daily issue then start looking for a problem. In that case go to the IAC and clean and troubleshoot. Good luck. Keep us updated.
 
Thanks for the replies, been without reception so haven't seen them til now. I will check the IAC when I have time, sounds like a good place to start. Over the past day it's been fine, it did the same thing upon start up once more after the first time, although even when it idles fine, the first initial take off after starting the engine up, it feels like the engine wants to stall for a second then it drives fine. On the past 5 cold start ups, it has idled fine so I'm less concerned.

To address some of the suggestions; it could be bad fuel, i've been through almost a whole tank then filled up again and it does seem to be mainly better so we'll see how that progresses, and we have been getting a lot of rain. Spark plugs have been replaced in the past 2000km or so, so ruling that out. Like i said, IAC is a good place to start if the problem persists. As for the vacuum leaks, what's the best way to address that?
 
Hammer24 said:
Thanks for the replies, been without reception so haven't seen them til now. I will check the IAC when I have time, sounds like a good place to start. Over the past day it's been fine, it did the same thing upon start up once more after the first time, although even when it idles fine, the first initial take off after starting the engine up, it feels like the engine wants to stall for a second then it drives fine. On the past 5 cold start ups, it has idled fine so I'm less concerned.

To address some of the suggestions; it could be bad fuel, i've been through almost a whole tank then filled up again and it does seem to be mainly better so we'll see how that progresses, and we have been getting a lot of rain. Spark plugs have been replaced in the past 2000km or so, so ruling that out. Like i said, IAC is a good place to start if the problem persists. As for the vacuum leaks, what's the best way to address that?
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I have a rough idle when the AC is on or when im in gear (auto) holding the brake. Did you end up fixing your issue?
 
Hammer24 said:
I did, it was the IAC as suggested by a few. Theres a great write up by chris here on the forum that I followed to get it better than ever
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I tried cleaning and also replacing mine. Didn’t work for me, sadly.
 
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