96 explorer 4.0 rough idle on every start

[mudbug0426]

i have a 96 explorer xlt 4x4 with a 4.0 ohv and it will not idle right.

it has 144,000 on it and the check engine light is on. i took it to autozone to have the codes pulled and there are two. p0174 and p0171. for each code they printed me a ticket saying what it means and the probable causes are.


ticket for p0171

definition - fuel trim bank one condition

explanation - the pcm uses the o2 sensor to calculate the air/fuel ratio of the engine. the computer has recognized a rich or lean condition on bank one only.

probable causes - 1. if bank one and two codes set together suspect fuel pressure or maf sensor.

2. o2 sensor defective

3. ignition misfire-repair

4. fuel injector problem



ticket for p0174


definition - fuel trim bank two

explanation - the ecm has detected a rich or lean air/fuel ratio condition on engine bank two.

probable causes - 1. if bank one and two codes are set together suspect a fuel condition or maf sensor fault.

2. failed H02S21

3. ignition misfire condition

4. fuel injector problem

5. engine mechanical condition



i have had this problem before but not to this extent. sometimes when i would start it 'cold or hot' it would idle a little rough for a few secs and be fine. since the check engine light first came on which has been almost if not a month now with these two codes, i have replaced the maf sensor, idle air control valve, the two o2 sensors before the cats, new fuel filter, new spark plugs and wires, the upper intake manifold gasket. im out of ideas now, im thinking and hoping its not a fuel pressure problem, when replacing the gasket i did take out the injectors one by one to make sure nothing was blocking the screen on the tips.


after replacing the maf sensor, is when it started to and now will idle horrible for roughly 20 to 30 seconds, then it will idle up to about 1100 to 1200 for a few secs and come back down to 1000 rpms and will idle fine until the next time i start it, and it will do the same thing all over again every time.

i have also checked for broken vaccume lines and they all look intact.

any ideas??

 

[team]

i would check your fuel pressure but you may end up needing lower intake manifold gaskets. ALso be sure and check for vacuum leaks (hoses, lines, etc.)

 

[mudbug0426]

how exactly do i check the fuel pressure? and now that you mention the lower intake gaskets, after starting, between that 20 to 30 secs of rough idle with the hood up i can hear something leaking like a vacume leak maybe? when the idle smoothes out that leaking sound goes away and i wont hear it again untill the next start.. does this every time. this is making me think its more of a gasket or vacume problem than a fuel problem.. any other ideas?

 

[96eb96]

the metal could be heating up and sealing the surfaces after you start the truck. For fuel checks you need a special pressure gauge tool. There is a tire type pressure valve on the fuel rail that you connect to.

 

[mudbug0426]

is there any way to see if those intake gaskets are leaking before i pull everything apart again, replace them and that not being the problem?

 

[rockoskates]

02 Sensor

I had this same exact problem. Replace all your O2 sensors, as they pretty much go out at about the same time. The problem should be fixed then. Also check your hoses and stuff too, it's all routine maintenance.

 

[mudbug0426]

rockoskates, i have replaced the two o2 sensors before the cats, but not the one after... what do you think the chances are that last sensor is causing this problem?

 

[mike96exlt]

I think maybe O2 also...

I think it could be that third O2 also...

I know I'm new to all this... but I remember years ago (not sure exactly how far back) I was having some problems similar to what you describe... I too went to Auto Zone and pulled to codes for the check engine light... which came back saying the O2 sensors were bad... using the Haynes manual, I replaced two of the O2 sensors... I don't think I knew there was a third???

Anyway... that didn't fix the problem and I ended up taking it into the shop... it turned out to be the third sensor... the one that I didn't replace...

 

[mudbug0426]

ok, well i just replaced that 3rd o2 sensor.. it helped a little bit but not enough for that to be the cause of the problem.. im going to drive it for a couple of days and see what happens. im also going to try and replace as many vaccume lines as i can get to with rubber hoses, none are cracked or broken that i can see but everytime i open the hood to do something i always seem to break another one so i might as well replace them.. does anyone have any tips on how to check for a vaccume leak?

 

[redbeard7]

I'm new here, and the same problem brought me here with my 01. Check out this thread, it pointed me in the right direction,. and it fixed my on-going problem.http://www.explorerforum.com/forums/showthread.php?p=1996156
Good luck with it.

Joe

 

[mudbug0426]

thank you joe, ill be reading up on that link you sent me and see what i can find

 

[uptownrockstar]

Hey guys this is my first post, here we go..

does anyone have any tips on how to check for a vaccume leak?

You use a vacuum gauge. You can get it at autozone i believe. you hook the noozle up to any vacuum port after the throttle body (any hole in the intake pleium), by disconnecting one of the pcv valves.

crank the engine. the gauge should read a steady 18-22ibs. if this is the case the engine is fine. NOTE= this test is an over all test, if the needle wobbles in any way during the test. there is a leak. where at is another question.

let me answer that for you. you have a vacuum leak. you can clearly hear it yourself.

use the mickey mouse method. get a tube. put your ear on one side and run the other side along the engine. the noise you hear will get louder when the hose detect the leak..

 

[rockoskates]

Plugs might be next

Have you replaced the spark plugs recently? If one of those isn't firing correctly, the engine has a tough time at idle. That could also explain why it's too rich/lean. If you do change the plugs, might as well change the wires as well. That'll take you the better part of an afternoon to do.

One word of advice if you do change the plugs...take the passenger side front tire off. It makes life SOOOO much easier than working around it.

Stupid broken socket wrench...

 

[SensRanger]

Hello,

I have a 96 Ranger 4.0 L OHV. I had low, rough idle and stalling at traffic lights and when stopped and idling in park. I also had codes P0171 and P0174. Dealer replaced Intake Gasket, no change in symptom. Kept it for 3 days! Finally diagnosed Rusted out EGR Tube. There was a small hole in the Tube near where it goes into the part that looks like a upside-down flying saucer. No one has mentioned EGR assembly yet, you may wish to consider it.
Replaced this Tube and all has been well since. Hope this helped. Good luck.

 

[mudbug0426]

uptownrockstar, good idea, i will get a vacuum gauge at autozone tomorrow and see what it reads. i will also replace any vacuum lines i can with rubber hoses. the only thing is the noise i hear is only present while it idles rough for that first 20 secs after startup, as soon as it smoothes out the sound goes away, and you can only hear it if you have your head under the hood, so its not too loud but is noticeable if your listening for it.. any idea why how or what could be leaking vacuum wise?

rockoskates, yes i have recently changed the spark plugs and wires, and the passesnger side wasnt too bad, took about an hour to change all six good idea about taking the front tire off, ill keep that in mind for the next set of plugs!

 

[mudbug0426]

sensranger, which gasket did the dealer replace? i just replaced my upper intake gasket with not much change, im wondering if all of this could be my lower gasket leaking of the intake manifold? i wish i would have replaced the lower at the same time i did the upper :/ i will also check the egr assembly tomorrow as well.

 

[SensRanger]

It was the upper intake gasket that was replaced, as far as I can remember. It was over 5 years ago. Check engine light has never come on ever since! The gasket was basically replaced because the dealer said "oh ya, 0171 and 0174 lean condition, you have an air leak at the upper intake, that's common" without really running a diagnostic. Of course, changing it did nothing, the gasket was fine. Then for some reason, it took them 3 days to find the rusted EGR tube. Yet when I looked at the old part, it was clear that it had a flaky-rust hole. The hole was facing down and away. I guess they took a while to break out the mechanic's mirror. At least they fixed it proper and I didn't have to bring it back (unlike my transmission woes- not at the dealer).

 

[mudbug0426]

im running out of ideas

well i just replaced most of the vacuum lines this afternoon, with no change. the ones i did not replace i could see there were no cracks, and the ones i did replace looked fine as well, so i think vacuum lines are checked off the list of things it could be.

i guess the next thing for me to do is check that egr tube your talking about.. do you have any idea what it takes to replace that tube? im thinking i might as well buy the lower intake gasket and replace it while i have the upper intake off since that seems to be the most difficult part 'taking it off and putting it back on' stupid egr tube

does anyone know if you have to take off the valve covers to get the lover intake manifold off??

 

[96eb96]

well i just replaced most of the vacuum lines this afternoon, with no change. the ones i did not replace i could see there were no cracks, and the ones i did replace looked fine as well, so i think vacuum lines are checked off the list of things it could be.

i guess the next thing for me to do is check that egr tube your talking about.. do you have any idea what it takes to replace that tube? im thinking i might as well buy the lower intake gasket and replace it while i have the upper intake off since that seems to be the most difficult part 'taking it off and putting it back on' stupid egr tube

does anyone know if you have to take off the valve covers to get the lover intake manifold off??

Those codes point to a gross air leak.

The valve covers do have to come off for the lower intake. I know there is a set which contains all gaskets for this repair.

Check the large black air intake tube for holes. Check the PCV valve, grommet and hoses.

Check the egr tube carefully first for any holes. It is a PITA to get off in a 96 cause of the heated corrosion. Good luck with those large fitting nuts. Get a good flexible MAPP torch to heat those things up.

Check your air sensor and coolant temp sensor to see they are reading correctly. You may need a scan tool or a voltmeter. If they are wrong the truck can think you are warmed up when you aren't.

If you do the gaskets I think you can get away with just unbolting the EGR, just spray some pentrating oil on the screws and it comes out.

Also, do you have a good scan tool? I would ask you to look at BARO, fuel trims, misfire counts... I can suggest a good one...www.obd-2.com pwm/iso combo.

Was your maf new or reman?

 

[mudbug0426]

wow 96eb96 thank you thats alot of info, buts try one thing at a time

im going to leave replacing the lower intake gaskets at a last resort if i can.

which intake tube are you talking about? i will check and replace the pcv palve tonight. the grommet and hoses looked ok.

when i replaced my upper intake gaskets, the egr tube was pretty nasty so i tried to clean it the best i could, but did not notice and holes or cracks.. but then again i was not looking for any.

which air sensor are you talking about?

and my temp gauge is no where near accurate, the needle always goes up and down and has done this for sometime now.. i know there are 2 sensors there, one the computer reads i guess and then the temp sensor? i have replaced the temp sensor about a year ago but did not replace the one on the left side, im guessing thats the one the computer reads.. ill replace that tonight..

no i do not have a scan tool tight on money right now but one day i will get one.

my maf sensor was a reman from autozone