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1998 explorer rough idle

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Old 12-13-2003, 12:12 PM
gto78 gto78 is offline
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1998 explorer rough idle

ok, 3 times now i've been extremely close to being hit head on by oncoming traffic due to a seemingly uncurable stalling problem. It idles rough sometimes, and other times it seems fine. BUT when sitting at a light, waiting to turn left after the oncoming traffic has a quick opening, I start to go, I get halfway across the intersection and then without warning, it dies completely. Now its too late to stop and back up- and the cars are flying head on towards you locking up they're brakes. One time I would have been killed by the 18 wheeler that was coming if I hadnt gotten it started and moving again just in time.

I replaced the IAC, the plugs, filters and wires, and the EGR valve. I checked everywhere for intake leaks and found nothing. Changed the O2 sensors since they had plenty of mileage on em. It idles like crap still, even after 30+ tanks of every kind of injector cleaner they make. We used the snap on scanner tool to monitor things and it never acted up then. The TPS seems to move smoothly, and fuel pressure was checked and found to be around 25-30 psi. Don't know if thats normal. The intake air temp was reading a constant 120 degrees F. I also checked the fuel cap to make sure it was closing completely. The dealer checked the TB for excessive clearance and said it was ok.

It seems to only stall like that after driving on the highway and then stopping at the first light after that.
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Old 12-13-2003, 12:17 PM
gto78 gto78 is offline
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one other thing, the FORD dealer in town supposedly changed the fuel pump and filter, saying it was the problem. They charged my girlfriend $1500 to do the job. A month later it was doing the same thing...... needless to say that dealer will never touch that truck again.
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Old 12-14-2003, 01:41 PM
gto78 gto78 is offline
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any ideas yet? I wish I had the shop manual for it. Especially on cd.
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Old 12-16-2003, 02:07 PM
randj randj is offline
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i think there was a tsb on this, you might search on that. there is a link from this site. it had to do with a vacuum problem...damn, i'm drawing a blank now. anyway, i had the same problem on just a few occasions, but mine magically disappeared. i remember they described the problem as most likely to occur after coming off cruising speed stopping, and making a left turn. mine never did die completely, but i would hit the gas, and it would surge, almost stall out, then grab back up and go. scary stuff.
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Old 12-16-2003, 04:56 PM
gto78 gto78 is offline
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thats exactly what happened to me, everytime making a left turn after driving on the highway, or driving at one consistant speed for more than a few min. You'd think the dealer would be able to pull that safety type of problem up on the computer, but they didnt find anything. I've asked a few ford mechanics who said normally these engines have bad iac valves and also vacuum leaks..... i'm goin to try harder in finding a vacuum leak. i definitely hear a loud hissing noise from the iac and also a lot of noise gets transmitted through that plastic intake. so its hard to tell, just keep sprayin the carb spray around the joints again...
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Old 12-16-2003, 06:49 PM
randj randj is offline
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i've just replaced my iac for another issue. i'd be curious to know if you find a vacuum leak and where. i was just like you last night in the garage, carb spray in hand. nothing.
let us know.
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Old 05-12-2012, 09:07 PM
Rich Dotterer Rich Dotterer is offline
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IAC Gasket won't seal

Hi Guys I am new Here brought out to this site because I am pulling my Hair out
I am Very Mechanically inclined and Have rebuilt the entire Brake system including Rotors front and rear W/ New Pads / Caliper brackets < these were the Best because the bolt heads turned to dust & out came the Grinder / front Hubs / sway bar links / emergency brakes & all new hardware kits / complete new exaust system W Cats Dual pipes & Muffler & tail pipe W/ resonator / O2 Sensors / Tranny flush / Hood Lift supports / Belt tensioner & Idler pully / Parking brake switch / Washer Pump Relays / 900 CCA 12V Battery / Etc .... on my Girlfriends 1998 Explorer Sport with the SOHC 4.0 Liter that she got from a Guy that should have givin her the truck, because I am up to about 2,000.00 in replacement parts that I had to install just to make it road worthy + $1,550.00 to buy it

I have for the Last Few Days been trying to get three different IAC's from Advanced Auto & Napa to seal Properly
Her Daughter was driving the truck and took a Left turn, it shuttered, and shut down, and would not stay running so it had to be towed to a Garage.

When I went to the garage, and started it up, I hadn't noticed any of the Problems her daughter had with it before it was towed
I noticed that her daughter had the A/C Switched on when I opened the Hood, and started I up, the Idle on the Motor didn't increase when the compressor clutch engaged
I knew at that point that the IAC was bad, and I could hear a slight hissing noise coming from the throttle body
I watched a few video's on how to do a Smoke test & carb cleaner to try to find a Vacuume leak, I sprayed the Carb Cleaner around under the hood, and it didn't provide any results, then remembering about the smoke test but didn't have a Smoke machine, I plugged off the throttle body, and Valve cover breather line with plastic bags, and I took the tube that goes into the plastic base of the IAC, and lit a Cigarette, and started blowing smoke into the tube..
Immediatly I saw smoke coming from under the IAC, and a Little bit coming out of the bottom EGR
I Then went to Adavanced Auto parts, and bought a New IAC
It didn't come with the figure 8 rubber gasket that was originally there but it was a Paper gasket material for $48.00
I mounted it up, and it leaked like a SOB with the cig. somke again.

I took it back ONLY to find out they gave me the "4.0 liter OHV" IAC part by mistake. Not the SOHC one
They switched it out, and added another $79.00 to the Tab, so now I was in it for $129.00 but it had the right gasket this time but the base plate was not flat like the original one I had on the truck
It had the figure 8 moulded in the metal base plate
Thinking I had it made, as this new one looked like it would seal right away
It too leaked like a SOB with the smoke.

So I took it back to Advanced Auto, and got one from Napa
This one had the Flat bottom Plate but no Figure 8 Gasket for $80.00
Mounted it up and again leaking like a
I tried using some small O Rings under the old Figure 8 gasket
I tried using the O Rings W/ some Cork lined Gasket Material single then doubled the cork and doubled the o rings & RTV silicone
I tried using some 3/4 gromets that I widdled down to fit in the figure 8 channel on the throttle body, and they were about 3/16th's taller then the plastic housing, and they crushed nicely when I tightened the IAC down BUT the same dam thing leaking like hell with the smoke

Funny thing is that I can plug the hole with my finger, and blow in the tube, and there's no leak what so ever
I did this because, I then thought as I was tightening the bolts that the intake housing where the IAC Mounts, must have a crack in it, and only leaked when the bolts were tightened

I am like ready to PUKE or put a rag in the tank and light it up !!!!!
Does anyone have any suggestion that I can try to seal this leak I am dealing with ???............. ????
Because this is killing me and it's driving me nuts
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Old 05-13-2012, 08:42 PM
Jasonx521 Jasonx521 is offline
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What is the vacuum at idle?

Test the PCV system:

1.) Take off the PCV intake hose/tube (from intake tube to valve cover) and plug both ends
2.) While the engine is idling; read the vacuum at the dipstick tube
- Vacuum reading should be ~ 1-3 in Hg

If it is higher than this; the PCV valve is most likely stuck open
If it is lower than this; either the PCV tubing and/or air/oil separator is leaking and/or the crankcase is leaking (gasket(s), seal(s), engine oil cap on valve cover etc.)

You can also take the PCV return vacuum line(s) off and plug the intake; If the idle smooths out and the hissing sound goes away, then you have a leak in the PCV system
- Make sure the PCV intake hose is attached like normal
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Old 05-13-2012, 09:03 PM
Rich Dotterer Rich Dotterer is offline
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Thanks for the Reply
I will have to go any buy a Vacuume gage to do these tests
Can you steer me to a Vacuume system Schematic Link??
so I can identify these components on the engine, because I am not familiar with the 4.0 SOHC component locations ??
I actually looked today for the PCV Valve ..
I have read that it's on the drivers side near the fire wall but I couldn't find it..but only spent a couple minuted looking for it..as I was more interested in finding something rubbing the colum

do you have any word on the stalling when making a Left turn I have read so much about ??
this is exactly what happened to my Girlfriends daughter when the truck stalled out on her, sending me on this wonderful adventure & or can you identify or have heard what makes the truck do this ??

I have looked at any wires that could be near the steering shaft but didn't see anything touching it
even though the IAC Is leaking, when I start up the truck, the Cold idle seems to have smoothed out from what it was doing, from Before when
A couple of weeks went by while I was getting Brake parts & installing them, when I started it up after I had it back down on the ground the Motor was sputtering like a Mother until i warmed up
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Old 05-13-2012, 09:50 PM
Jasonx521 Jasonx521 is offline
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I'm not sure about the turning thing, but I would suspect it has more to do with the engine trying to accelerate than turning. I would venture to say that when you at a low speed or stopped and you try to accelerate close to or at wide open throttle it should reproduce it. It happen when the engine is cold (intake gasket i.e. vacuum leak) or hot (faulty spark plug wires that arc to the engine block or ground when hot)

The above is speculation on what I know about the said explorer.

I own a 2000 SOHC; for the most part the 98 and 2000 are the same

If the IAC gasket is leaking, then while idling you should be able to spray starter fluid at the suspected leaking area and it should affect the engine (rev up or smooth out)

I would start check for vacuum leaks;

1.) test with starter fluid, (use something to block a majority of the wind from the fan over the top of the engine)

2.) test PCV system

3.) Use a smoke bomb like you did with the cig, except use small fan and blow it intake and then the crankcase (Of course blocking known holes)
- Try using a black light, (not sure if all smoke will show up w/ black light)

*** if the above does not produce a problem, then I would replace the spark plugs and wires (Motorcraft seems to be the most reliable) You could replace the coil, but most likely not the source (need a O-scope and signal gen. to test properly)

The MAF, IAC, O2, TPS, TEMP, EGR, DPFE sensors need to be cleaned and tested.

I once had a TPS go bad on a TJ jeep, it would idle fine, and work fine at WOT, but any sudden change in throttle in between it would hesitate bad. This was reproducible every time though

The PCV valve should be directly behind the intake (2" below top of upper intake and tight against back side of lower intake (close to top of lower intake)
The PCV hoses will connect to both the driver and pas. side on the back of the upper intake with ~3/8" vacuum hose (the hoses are split with a TEE fitting right on top of the PCV valve)

Google (w/ images) part number: F77Z-6C342-AB (this is the PCV valve assembly)

Vacuum gauge testing: How to Use and Interpret a Vacuum Gauge

PCV Info & testing: Positive Crankcase Ventilation (PCV)
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Old 05-28-2012, 10:50 AM
Rich Dotterer Rich Dotterer is offline
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Thanks JasonX521 that was very helpful for sure
Now I am reporting back here again on my Next Issue

well guys I found the source of the Vacuum leak
there was a Y shaped rubber hose that is hooked to the IAF port and the line coming from the intake/MAF inlet that feeds the throttle body and had a split in the bottom of it
Ford wanted $215.00 for this little rubber hose so I got some flexable 1" hose and installed it (NO MORE LEAK)
Next thing I am dealing with now is that I gave the Truck back to my friends Daughter
SHE DROVE IT FOR 2 DAYS and the Same thing happened again when she was driving on the Highway, and was leaving the off ramp after being stopped at a light, while she was making a Left turn the Engine shut down and would not start again
it would crank / sputter /and die again Etc. but would not stay running
but after she waited an hour on the side of the road, the engine started normally she was able to drive it, she parked it at a store.
I went to see what was happening with it, and it started right up, and I drove it 25 miles at 70 mph. back to my house and I made a couple left turns
one of them pretty hard and it never stalled for me ??
I did note only one thing that the tranny shifted pretty hard back into 1rst. gear with a thud when I was coming to a stop..
I can see nothing loose
I moved the plug wires around Etc.
The only thing I can see on the Web is change the plug wires next
Here's my question
I was reading about the Fuel pump enertia cut off switch in these vehicles
It seems to only stall when taking a left turn
what do you guys know about these switches ??
could that be causing this if the enertia switch was bad and telling the fuel pump to shut down on a left turn
Is there anyone out there that has knowledge about this Turning left issue ???
and if so what they did to fix this problem
I would lve nothing better then to throw another Grand at this problem (heh)(heh)
But I really would like to hear what you guys think or know about before I keep throwing parts at it, and have the same thing happen again & again........
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Old 05-28-2012, 11:37 AM
Jasonx521 Jasonx521 is offline
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I don't have much time to think about this, but have you check the fuel pressure? Maybe the fuel pump is weak? and after it hot it can produce enough pressure to even run?

If it is like mine (return-less system) my pressure is specified to be at ~60-65psi at all times

I'm not sure if its the other system; which would also have a fuel pressure regulator. I'm going off memory, but I believe this system pressure should be at ~ 40psi

In theory its: fuel, air, spark?
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Old 05-28-2012, 12:58 PM
Jasonx521 Jasonx521 is offline
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Here is a bulletin I found:

Publication Date: SEPTEMBER 21, 2000

1997-2000 EXPEDITION
1997-2001 EXPLORER
1998-2000 NAVIGATOR

A hesitation on acceleration or while turning may be felt on some vehicles. This may be caused by fuel pump cavitation due to fuel sloshing away from the filter sock in the fuel tank reservoir.


To service, check fuel pressure. Check all fuel pump related electrical circuits. If a fuel pressure concern is verified, refer to the following Service Procedure for details.


Attempt to verify if fuel pressure drops during the event.
If a fuel pressure drop is verified, check all fuel pump related electrical wiring, connections and related systems.
If all checks OK, replace the fuel pump/sender assembly with a revised fuel pump/sender assembly. Refer to the parts listing for application.
Refer to the appropriate model year Workshop Manual, Section 310-01, for removal and installation instructions.

F7PZ-9H307-BD Fuel Pump - 1997-1998 Explorer/Mountaineer (All)
XL2Z-9H307-AJ Fuel Pump - 1999-2001 Explorer/Mountaineer (All)
XL1Z-9H307-AB Fuel Pump - 1997-2000 Expedition (4X4)
XL1Z-9H307-BB Fuel Pump - 1997-2000 Expedition (4X2 With Base Suspension)
XL1Z-9H307-CB Fuel Pump - 1997-2000 Expedition (4X2 With Air Suspension)
XL1Z-9H307-DB Fuel Pump - 1998-2000 Navigator (4X4)
XL1Z-9H307-FB Fuel Pump - 1998-2000 Navigator (4X2)



Information Only


404000, 609000, 609500, 610000, 610500, 611000, 611500, 614000, 614500
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