Rough Idle

[Zackie]

I swear, Issue after issue on my sport, Yesterday my Explorer started running really rough, When I first start it and when its at temp it idles HORRIBLE, It shakes big time and the rpms fluctuate between 400 - 700 RPMs, And it stumbles and pops out the exhaust when I first start moving, But once i'm past about 1000 RPMs it runs like theres no problem, Anyone else have this issue with the 4.0 SOHC?

 

[swshawaii]

Disconnect the idle air control (IAC) electrical connector while the engine is running and see if there's a change in idle. If no change it may need cleaning or replacing. The rubber PCV elbow under the plastic throttle body cover should be checked on your 20+ year old Sport. (Disregard if you have an early 2001 "Job 1" engine) Check engine light or p0171 & 174 trouble codes are NOT always present with a faulty PCV elbow. If you have the earlier Job 1 engine with the oil fill on the driver side, leaking intake gaskets are a very common problem. GL

P0171 & P0174 4.0L SOHC's Sport/Sport Trac

There are regular posts looking for answers to the P0171/P0174 DTC's. The 2001-2003 Sports and 2001-2005 Sport Tracs are legendary for throwing the codes together. Although there ARE instances where intake gaskets, among other issues, are the cause the overwhelming majority of these codes are...

www.explorerforum.com

 

[Pete Deering]

I swear, Issue after issue on my sport, Yesterday my Explorer started running really rough, When I first start it and when its at temp it idles HORRIBLE, It shakes big time and the rpms fluctuate between 400 - 700 RPMs, And it stumbles and pops out the exhaust when I first start moving, But once i'm past about 1000 RPMs it runs like theres no problem, Anyone else have this issue with the 4.0 SOHC?

You have a few thing going on.
1.When I first start it and when its at temp it idles HORRIBLE,
How do you know it up too operating temperature?
Do you have scan tool that does live data?
2 It shakes big time and the rpms fluctuate between 400 - 700 RPMs,
Check the mass air flow sensor, air filter and box, intake hose, air intake sensor, throttle body etc too see if they are clean, clear and tight seal no leak
3. And it stumbles and pops out the exhaust when I first start moving,
This cause by the car running rich , the O2 sensor shut off the fuel pump on and off when moving.
? Was your spark plug changed recently?
4., But once i'm past about 1000 RPMs it runs like theres no problem,
This is cause by a small air intake leak. It shows at idle but not at higher RPMs.
The fuel trims will show this change.

 

[Zackie]

Rubber PCV elbow should be the FIRST thing to check on your 20+ year old Sport. (Disregard if you have an early 2001 "Job 1" engine)
Check engine light or p0171 & 174 trouble codes are NOT always present with a faulty PCV elbow. GL

P0171 & P0174 4.0L SOHC's Sport/Sport Trac

There are regular posts looking for answers to the P0171/P0174 DTC's. The 2001-2003 Sports and 2001-2005 Sport Tracs are legendary for throwing the codes together. Although there ARE instances where intake gaskets, among other issues, are the cause the overwhelming majority of these codes are...

www.explorerforum.com

Unfortunately not the case, Replaced it along with the other elbow not even a ago along with the PCV valve, Took them off and checked both, Both seem to be fine as well

 

[Zackie]

You have a few thing going on.
1.When I first start it and when its at temp it idles HORRIBLE,
How do you know it up too operating temperature?
Do you have scan tool that does live data?
2 It shakes big time and the rpms fluctuate between 400 - 700 RPMs,
Check the mass air flow sensor, air filter and box, intake hose, air intake sensor, throttle body etc too see if they are clean, clear and tight seal no leak
3. And it stumbles and pops out the exhaust when I first start moving,
This cause by the car running rich , the O2 sensor shut off the fuel pump on and off when moving.
? Was your spark plug changed recently?
4., But once i'm past about 1000 RPMs it runs like theres no problem,
This is cause by a small air intake leak. It shows at idle but not at higher RPMs.
The fuel trims will show this change.

I have a Scan tool that shows the live data, It fluctuating big time, Air filter was replaced not to long ago and was checked when this just started, I did notice in the live data one of the O2 sensors are reading way different compared to the other, One of the Two before the cats, Which if thats the case, is gonna be a pain to swap, Currently in Class, Will send a photo of the OBII data later, Also just did a tune up on it including the wires and plugs a couple weeks ago, Which at the time was running a little rough, But not 8 mpg rough like it is now (rough esimate, did the calculating at the pump yesterday) , But its gotten bad now, And the intake leak I figured, I noticed on the live data its close to tripping the check engine light, That i was gonna take care of when I get paid next Monday

 

[swshawaii]

No stored trouble codes? My bet's on intake gaskets, but you may want to do a smoke test to be sure.

As mentioned in my edited first post, disconnect the IAC plug with the engine running.

Pete Deering offers excellent advice and troubleshooting.

 

[Zackie]

No stored trouble codes? My bet's on intake gaskets, but you may want to do a smoke test to be sure.

As mentioned in my edited first post, disconnect the IAC plug with the engine running.

@Pete Deering offers excellent advice and troubleshooting.

Only trouble codes stored are the 4x4 codes, IAC I just replaced, I'll disconnect it after school and see what happens before I head home, For the smoke test I have no way of doing unfortunately, But, I was planning on checking them as I'm the second owner of my sport, my aunt being the first and she said that they've never been touched, And I've been told they're trouble when it comes to these 4.0 SOHC motors so I wanna play it safe yknow?

 

[Pete Deering]

I have a Scan tool that shows the live data, It fluctuating big time, Air filter was replaced not to long ago and was checked when this just started, I did notice in the live data one of the O2 sensors are reading way different compared to the other, One of the Two before the cats, Which if thats the case, is gonna be a pain to swap, Currently in Class, Will send a photo of the OBII data later, Also just did a tune up on it including the wires and plugs a couple weeks ago, Which at the time was running a little rough, But not 8 mpg rough like it is now (rough esimate, did the calculating at the pump yesterday) , But its gotten bad now, And the intake leak I figured, I noticed on the live data its close to tripping the check engine light, That i was gonna take care of when I get paid next Monday

1. Air filter, my thinking, nice nest.
2. Spark plugs, my thinking: if you drop a plug when changing it, the gap could be closed. no spark, not firing.
3. The 8 mpg, maybe cause by a dirty EGR valve.
4. You need to find out which bank is running rich. Which O2 sensor side?
5. Is the operating temperature from the scan tool? my thinking: bad coolant temperature sensor. But if the fuel trim is only off on one bank than it probably air leak on that bank.

 

[Zackie]

1. Air filter, my thinking, nice nest.
2. Spark plugs, my thinking: if you drop a plug when changing it, the gap could be closed. no spark, not firing.
3. The 8 mpg, maybe cause by a dirty EGR valve.
4. You need to find out which bank is running rich. Which O2 sensor side?
5. Is the operating temperature from the scan tool? my thinking: bad coolant temperature sensor. But if the fuel trim is only off on one bank than it probably air leak on that bank

Best way to put it on the Sensors is they were labeled, Dont remember atm and wont be able to check till I get home as its my dads scanner, So it'll be at least 4 hours before I can check

 

[J_C]

With one of the upstream sensors reading a lot different, I'd suspect either the sensor itself, or it's reading correctly, a problem with the cylinder bank it's on and that bank has a misfire(s), which could be any number of things but intake manifold vac leak seems as likely as anything, if you don't find something else.

Edit: More info was posted since I started this post. I'd investigate the spark plugs like whether it runs the same or worse if you unplug a wire from the coil pack. If worse that's not the right one. If no worse, then there's a potential problem on one of the two cylinders fed by this waste spark system.

I'd first hook up a scan tool and look at long term fuel trims and go from there. Regardless if you haven't cleaned out or replaced your IAC in recent years, it is probably due for it, but that would affect idle far more than taking off driving.

 

[Zackie]

With one of the upstream sensors reading a lot different, I'd suspect either the sensor itself, or it's reading correctly, a problem with the cylinder bank it's on and that bank has a misfire(s), which could be any number of things but intake manifold vac leak seems as likely as anything, if you don't find something else.

Edit: More info was posted since I started this post. I'd investigate the spark plugs like whether it runs the same or worse if you unplug a wire from the coil pack. If worse that's not the right one. If no worse, then there's a potential problem on one of the two cylinders fed by this waste spark system.

I'd first hook up a scan tool and look at long term fuel trims and go from there. Regardless if you haven't cleaned out or replaced your IAC in recent years, it is probably due for it, but that would affect idle far more than taking off driving.

I replaced the IAC about, Two-Three weeks ago, It would not idle till I replaced it before, Then it was fine for a good while till the tune up, And now here we are

 

[Pete Deering]

Best way to put it on the Sensors is they were labeled, Dont remember atm and wont be able to check till I get home as its my dads scanner, So it'll be at least 4 hours before I can check

I thinking, it could be a intake manifold vacuum leak on that bank. Spray some carb cleaner or starting fluid or brake clean on that side bank intake manifold and see what happens.

 

[Zackie]

With one of the upstream sensors reading a lot different, I'd suspect either the sensor itself, or it's reading correctly, a problem with the cylinder bank it's on and that bank has a misfire(s), which could be any number of things but intake manifold vac leak seems as likely as anything, if you don't find something else.

Edit: More info was posted since I started this post. I'd investigate the spark plugs like whether it runs the same or worse if you unplug a wire from the coil pack. If worse that's not the right one. If no worse, then there's a potential problem on one of the two cylinders fed by this waste spark system.

I'd first hook up a scan tool and look at long term fuel trims and go from there. Regardless if you haven't cleaned out or replaced your IAC in recent years, it is probably due for it, but that would affect idle far more than taking off driving.

Just got out of school, unplugged the IAC and it wouldn’t run at all, plugged it back in and it fired right up

 

[Zackie]

Actually found a older forum on here that explains my issue pretty well

4.0 SOHC Occassional Rough Idle

Hey everyone. Just bought my dad a 2000 Explorer Eddie Bauer 4.0 SOHC V6. I absolutely love it, its a great vehicle. 257,000kms with a rebuilt transmission, new spark plugs and a new exhaust. Got the entire truck for $850!!!! Only problem is as follows: After the truck warms up a bit, and your...

www.explorerforum.com

 

[Zackie]

With one of the upstream sensors reading a lot different, I'd suspect either the sensor itself, or it's reading correctly, a problem with the cylinder bank it's on and that bank has a misfire(s), which could be any number of things but intake manifold vac leak seems as likely as anything, if you don't find something else.

Edit: More info was posted since I started this post. I'd investigate the spark plugs like whether it runs the same or worse if you unplug a wire from the coil pack. If worse that's not the right one. If no worse, then there's a potential problem on one of the two cylinders fed by this waste spark system.

I'd first hook up a scan tool and look at long term fuel trims and go from there. Regardless if you haven't cleaned out or replaced your IAC in recent years, it is probably due for it, but that would affect idle far more than taking off driving.

O2B1S1 is reading way off from the rest, These are the O2 sensors, O2B2S1 is the downstream O2 sensor

 

[J_C]

^ This seems contradictory as previously you wrote " I did notice in the live data one of the O2 sensors are reading way different compared to the other, One of the Two before the cats".

The O2 sensor before the cat (between the cat and the engine) is the upstream sensor and has more impact on engine operation. The one after the cat (towards the tailpipe) is the downstream and does not impact engine operation much, if at all.

It depends on the scan tool understanding the positions correctly, but O2B2S1, should be the bank 2, upstream (#1) sensor. 02B2S2, should be the downstream (#2) sensor.

Regardless, if it is the upstream sensor, it still could be either the sensor is bad or the engine is misfiring. Considering the age of the sensors, it might be worth going ahead and replacing both upstream sensors anyway, disconnect battery to lose PCM saved parameters and force a re-learn.

 

[Zackie]

^ This seems contradictory as previously you wrote " I did notice in the live data one of the O2 sensors are reading way different compared to the other, One of the Two before the cats".

The O2 sensor before the cat (between the cat and the engine) is the upstream sensor and has more impact on engine operation. The one after the cat (towards the tailpipe) is the downstream and does not impact engine operation much, if at all.

It depends on the scan tool understanding the positions correctly, but O2B2S1, should be the bank 2, upstream (#1) sensor. 02B2S2, should be the downstream (#2) sensor.

Regardless, if it is the upstream sensor, it still could be either the sensor is bad or the engine is misfiring. Considering the age of the sensors, it might be worth going ahead and replacing both upstream sensors anyway, disconnect battery to lose PCM saved parameters and force a re-learn.

Yeah I was a bit confused, Sorta new to this stuff, I’ll give the PCM a reset and I was planning on doing O2 sensors eventually since I just rolled 100K miles