Rough idle/low RPMs and intermittent stalling at low speeds - JeepForum.com
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post #1 of 16 Old 11-19-2019, 10:51 AM Thread Starter
JHogg11
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Rough idle/low RPMs and intermittent stalling at low speeds

I’ve been having the issue in the thread title for a few weeks on my 2004 4.0 WJ. In the last month or so, I’ve replaced the following:
- Battery
- Spark plugs
- Throttle Position Sensor
- Idle Air Control Valve
- Serpentine belt

I’ve also cleaned out the throttle body (last night) and added Lucas Oil Fuel Treatment to hopefully clean out the fuel injectors, although I’ve only gone through about 1/3 of a tank of gas since doing that.

One thing I noticed while replacing/cleaning the parts is that the old IAC and its plug, which is still in the vehicle, had chunks taken out of them. The air intake resonator also had a chunk taken out of it on the side facing the IAC. I think the missing chunk on the resonator is covered up by the rubber piece that connects it to the throttle body, but I wonder if that could be causing a vacuum leak. It’s a pretty weird thing, almost like there was a small explosion in that area. I noticed the IAC previously, but I just noticed that the air intake resonator was damaged last night.

Here are what I think are the important details/symptoms of the issue:
- Low RPM idling seems to occur only after engine has warmed up for a few minutes
- Vehicle idles at ~500 RPMs or slightly less. I believe the number should be 600+ based on past experience.
- Low RPMs are accompanied by minor/moderate vibration
- RPMs drop by about 100 (i.e., from 600 to 500) when transitioning from a very slow creep to a dead stop. This might be normal and maybe only the RPM values are low.
- If RPMs are low, putting the vehicle in park brings them back up. Again, this may be normal.
- Vehicle has shut off several times at rolling speeds. I think this is happening specifically while braking/decelerating, rather than purely rolling or slowly accelerating.
- There is an occasional feeling of low power/responsiveness when accelerating. Also, on several occasions, the vehicle has sharply lost power while accelerating at ~30+ mph, but it has not turned off at that speed.

As mentioned, I just cleaned the throttle body last night. Prior to doing so, the RPMs would sometimes tick back up after falling to 500 RPM, however, that didn’t seem to be happening on the way to work today, although it felt a little smoother at the lower RPMs and while accelerating from stop, but I might be overthinking that a bit.

One last thing I noticed this morning was that my fuel economy was fairly decent on the way to work. The mpg had been reset to 0.0 when I disconnected the battery last night, but by the time I got to work it was above where I think it normally is and my commute has a lot of stoplights.

I’m really trying to keep this thing together a little longer. Any suggestions are appreciated.

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post #2 of 16 Old 11-19-2019, 11:13 AM
Ross
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vacuum leak. get some starting fluid spray or similar (be safe) and spray around.

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post #3 of 16 Old 11-19-2019, 12:00 PM Thread Starter
JHogg11
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Originally Posted by Ross View Post
vacuum leak. get some starting fluid spray or similar (be safe) and spray around.
Okay, thanks for that suggestion. Anything I said specifically that makes you think itís a leak rather than something else?
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post #4 of 16 Old 11-19-2019, 12:24 PM
jtec
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the RPM trending lower does not suggest a Vac leak - but the suggestion to check it using the old school spray trick is to easy and fast to ignore.

When slow creep to dead stop causes the RPM issue - shift to N - did the RPM recover?

Every time you start the vehicle does the CEL (Check Eng Light) come on @3 seconds then go off?

Tell us is the Air Bag light on and does it complete the Bulb test at every start - same as above.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #5 of 16 Old 11-19-2019, 12:52 PM Thread Starter
JHogg11
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Quote:
Originally Posted by jtec View Post
the RPM trending lower does not suggest a Vac leak - but the suggestion to check it using the old school spray trick is to easy and fast to ignore.

When slow creep to dead stop causes the RPM issue - shift to N - did the RPM recover?

Every time you start the vehicle does the CEL (Check Eng Light) come on @3 seconds then go off?

Tell us is the Air Bag light on and does it complete the Bulb test at every start - same as above.
I will have to check neutral on the way home later, but the RPMs do recover when switching to park. Does that effectively answer your question?

When I put the key in and turn it without actually turning it on, the check engine light is on but I think thatís normal. As soon as I turn it on, the check engine light turns off.

One other point on check engine codes, I actually had the spark plugs replaced at a repair shop. I had an engine misfire (code P0302) and the idling got really bad. I had already ordered the replacement IAC, so I took it in after that didnít work. Turned out to just be spark plugs, but I also had another code, P0135 - O2 Sensor Heater Circuit Bank 1, Sensor 1, that originally showed up alongside the misfire code, but the mechanic said that only the misfire code was there when I took it in. I figured that replacing the IAC made it go away but maybe thereís another issue there.

I will also have to check the airbag light. When you say bulb test, you mean coming on at 3 seconds? That doesnít sound familiar but Iíll check.
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post #6 of 16 Old 11-19-2019, 02:47 PM Thread Starter
JHogg11
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Okay, I tried switching it to neutral and the RPMs do tick back up to 600 and stay there even when I switch back to drive, at least for a minute or two while sitting at a light.

What does that indicate?
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post #7 of 16 Old 11-19-2019, 02:53 PM Thread Starter
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Is there anyway this could be a battery connection issue? I say that because itís had more trouble starting today since I disconnected and reconnected the battery last night.
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post #8 of 16 Old 11-19-2019, 05:08 PM
jtec
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As I mentioned above I am not thinking a VAC leak,

You are doing the basics, It is routine to clean the IAC, replace plugs, as I asked what type of plugs as brand matters and I often see the wrong type.
And you addressed the 2 codes- first the misfire P030x and the p0135, The o2 sensor code is gone hopefully.

Check your battery connections and stop removing cables as this dumps presets and stored info ie freeze frames and any codes

I was thinking the issue slowing and comming to a stop, causing a stall, rough idle sounds to me like a TCC issue, that was why I would look at trans and shifting to N. A scanner to look at codes as some trans codes will NOT display with key trick.

Anything you can add about transmission - you do use only ATF+4 and the level is checked you have performed routine replacing filter.

check battery connection stop disconnecting battery as it dumps presets, stored data such as freeze frame, codes pending and current. And if viewing live data it is not as accurate as readings/settings developed over time.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 16 Old 11-19-2019, 08:30 PM Thread Starter
JHogg11
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Quote:
Originally Posted by jtec View Post
As I mentioned above I am not thinking a VAC leak,

You are doing the basics, It is routine to clean the IAC, replace plugs, as I asked what type of plugs as brand matters and I often see the wrong type.
And you addressed the 2 codes- first the misfire P030x and the p0135, The o2 sensor code is gone hopefully.

Check your battery connections and stop removing cables as this dumps presets and stored info ie freeze frames and any codes

I was thinking the issue slowing and comming to a stop, causing a stall, rough idle sounds to me like a TCC issue, that was why I would look at trans and shifting to N. A scanner to look at codes as some trans codes will NOT display with key trick.

Anything you can add about transmission - you do use only ATF+4 and the level is checked you have performed routine replacing filter.

check battery connection stop disconnecting battery as it dumps presets, stored data such as freeze frame, codes pending and current. And if viewing live data it is not as accurate as readings/settings developed over time.
Just to put it out there, Iím learning as I go with this stuff. Iíve probably learned more in the last few weeks about how my vehicle works than the rest of my life combined, only because Iím trying to keep it alive, but Iím still pretty ignorant about most of it.

With that said, itís been downshifting rough for a while at lower speeds. When I say a while, I mean like several years, but itís never really gotten much worse. Usually the rough shift is while braking harder under around like 15 mph whereas the stalling is more like slowly braking while rolling. Thereís one spot on my commute home where I have to drive through several stop signs that are close together so itís like accelerating and slowing successively and thatís where I hear it rough shift a lot. The stalling tends to happen in parking lots where thereís less acceleration.

I have a scanner and there havenít been any codes or check engine lights since the two I mentioned.

And I honestly donít think any transmission-related maintenance has been done in a while.
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post #10 of 16 Old 11-20-2019, 06:26 AM
Ross
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Quote:
Originally Posted by jtec View Post
As I mentioned above I am not thinking a VAC leak,

You are doing the basics, It is routine to clean the IAC, replace plugs, as I asked what type of plugs as brand matters and I often see the wrong type.
And you addressed the 2 codes- first the misfire P030x and the p0135, The o2 sensor code is gone hopefully.

Check your battery connections and stop removing cables as this dumps presets and stored info ie freeze frames and any codes

I was thinking the issue slowing and comming to a stop, causing a stall, rough idle sounds to me like a TCC issue, that was why I would look at trans and shifting to N. A scanner to look at codes as some trans codes will NOT display with key trick.

Anything you can add about transmission - you do use only ATF+4 and the level is checked you have performed routine replacing filter.

check battery connection stop disconnecting battery as it dumps presets, stored data such as freeze frame, codes pending and current. And if viewing live data it is not as accurate as readings/settings developed over time.

What scanner would you recommend? I have a very basic one, I know there are ones that will read more the my basic scanner will read and thanks for the help with my kids XJ!!

01TJ33sWarn,ARBs F&R,bellyup,4.0,4.56s,5spd
99 XJ33sWinch,Electric locker up front,4.56s,4.0Auto
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post #11 of 16 Old 11-20-2019, 07:07 AM
jtec
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you want ALL codes, generic as well as manufacturers specific codes, ability to view live data- items such as ECT, TPS, MAP, O2 voltages, fuel trims, if system in closed or open loop, emission monitors ready or not ready.

The ability to see ABS is a price comparison how much more and SRS codes might not be a needed DIYer expense.
Ross likes this.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #12 of 16 Old 11-20-2019, 10:44 AM
Ross
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Quote:
Originally Posted by jtec View Post
you want ALL codes, generic as well as manufacturers specific codes, ability to view live data- items such as ECT, TPS, MAP, O2 voltages, fuel trims, if system in closed or open loop, emission monitors ready or not ready.

The ability to see ABS is a price comparison how much more and SRS codes might not be a needed DIYer expense.
I am not concerned about ABS (I am assuming anti lock brakes) but the other info you speak would be helpful. Would something like this to all of that/

https://www.amazon.com/LAUNCH-CReade...PCRXCJZ6S4RYEX

01TJ33sWarn,ARBs F&R,bellyup,4.0,4.56s,5spd
99 XJ33sWinch,Electric locker up front,4.56s,4.0Auto
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post #13 of 16 Old 11-20-2019, 12:36 PM Thread Starter
JHogg11
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Location: Charlotte
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My Jeep has been running much smoother today. Iíve only had the decreased RPMs issue once or twice out of maybe 30-40 stops. Yesterday it was nearly every time after the engine got warmed up. I wonder if cleaning the throttle body had a delayed benefit.

However, it still turned off on me once, so Iím wondering if the low/rough idling and stalling are two separate issues. Originally, I thought the issue might be related to the battery connections, although the transmission could make some degree of sense considering the rough shifting Iíve had for a while under fairly similar conditions (the shifting problem is most noticeable at low speeds when braking firmly). I always figured the transmission would be the death of the vehicle.

Iím planning to take it in Friday. Any other suggestions based on the above info are still welcome.
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post #14 of 16 Old 11-20-2019, 01:13 PM
Ross
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Quote:
Originally Posted by JHogg11 View Post
My Jeep has been running much smoother today. I’ve only had the decreased RPMs issue once or twice out of maybe 30-40 stops. Yesterday it was nearly every time after the engine got warmed up. I wonder if cleaning the throttle body had a delayed benefit.

However, it still turned off on me once, so I’m wondering if the low/rough idling and stalling are two separate issues. Originally, I thought the issue might be related to the battery connections, although the transmission could make some degree of sense considering the rough shifting I’ve had for a while under fairly similar conditions (the shifting problem is most noticeable at low speeds when braking firmly). I always figured the transmission would be the death of the vehicle.

I’m planning to take it in Friday. Any other suggestions based on the above info are still welcome.
My kids XJ had multiple issues with hard starts, idling and keeping it running.

Hard starts at operating temp was fixed by new fuel pump. Fuel Pressure was low so that one was a no brainier.

Rough idle and sometimes staling at idle would be an issue, cleaning the IAC valve worked for a couple days but then the problem came back so I replaced it. That helped allot.

I got code 0120 and had some gas pedal and idle issues. A new, TPS fixed that.

Still didn't start as easy or didn't idle as smooth as my TJ. When I took of the air intake it ran better like my TJ. When we first got the XJ it had a big *** K&N cone on it. We do some water crossing so it had to go. I though back I realized we didn't have idle issues with the big K&N. The stock air box I replaced it with was from a different year that seemed to be designed to hook up with something that sucked air in form behind the head light unlike the one we have. I also realized he had a larger after market throttle body.

I enlarged the hole on the stock airbox and that also really really helped.

It seem now everything is running really well now. After going though this we did pick up some additional MPG (about 4 mpg according to the computer).

It start fine now but still not as easy as my TJ. I have noticed that if I just press the gas a little it fires up even easier, but it idles and runs great now. I don't know if there is something else I should do or if it is as good as it needs to be.

As I read new posts about my issues other things pop into my head. After I replace the sensors we did have some occasional idle/stalling issues but far less often. After starting it and going into Reverse, Neutral, Drive and back to Reverse seemed to fix it as did driving it for about 20 seconds. However, since we enlarged the air hole on the box we haven't had any more issues.

Who knows what tomorrow will bring.

I di have a Chevy S10 where the idle would lower when you hit the brakes. A new brake master cylinder fixed that.

01TJ33sWarn,ARBs F&R,bellyup,4.0,4.56s,5spd
99 XJ33sWinch,Electric locker up front,4.56s,4.0Auto
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post #15 of 16 Old 11-21-2019, 06:23 AM
jtec
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you added the poor shift issue now - I posted above
"Anything you can add about transmission - you do use only ATF+4 and the level is checked you have performed routine replacing filter."

have you even checked the trans fluid level, color, look for particles looks like a silver paint in fluid?


This is an AUTOMATIC you are not shifting it yourself manually?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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