I have a 1999 B4000 4.0L with 160K miles on it. Bought the truck new. Up until about a year ago it ran perfect but has developed an idle, stalling and occassional jerky ride problem. It occurs at any temperature, engine hot or cold, A/C clutch on or off and in Park, Drive or Neutral. When you start the engine it will not idle unless you keep your foot on the gas. The idle speed will drop to 200-300 rpm and the engine dies. Sometimes you can barely tap the gas pedal and the rpm will shoot up to normal idle speed (about 900 rpm) and stay there a few seconds then begin to drop again. If the engine is cold it will often die a couple times after starting even with the foot on the gas and then about the 2nd or 3rd time run with your foot on the gas. At stop signs and red lights you have to keep your foot on the gas to keep it running. If you are approaching a stop sign and take your foot off the gas to coast to a stop and brake, the engine rpm will drop and the engine will die. It always starts fine though. Once you are driving it generally runs just fine at low or high speed. You can generally set the cruise control on the expressway and cruise right on. However, sometimes all of a sudden the truck will start bucking and jumping as if it has a terrible misfire. It usely lasts a few seconds and quits. Often if you step on the gas it quits. Even less occassionally the engine will begin to slow as if it is starved for fuel and slow down. You can press the pedal to the floor and it sputters a bit then picks up and runs fine.

I have read about all the threads in this forum and others and tried some of the suggested fixes but it still has the problem. I have tuned it up with new plugs, wires, fuel filter, air filter and PCV valve. Based on some of the forums advice I have replaced the IAC valve, the EGR valve and EGR Pressure Feedback Sensor, and cleaned and inspected the MAF sensor with MAF cleaner. I have checked all my vacuum lines and no leaks there and checked the engine timing which is fine. Fuel rail pressure and engine compression are also fine. Spark plugs show no clues, exhaust is clean and the engine uses virtually no oil. There has been no tear down on the engine like removing the heads, cam, timing gears or any of that and the engine is completely stock.

It shows no codes related to the problem. Two or three months after the problem started I showed a code that indicated an injector problem, traced the problem to a bad injector, replaced the faulty injector and it was fine. That took care of that code but didn't help the idle problem.

In my younger days I was into drag racing and I rebuilt engines, swapped transmissions, etc. and still do my own tune-ups today so I am fairly familiar with auto repair and have most of the tools for testing newer cars but this one stumps me. As a last resort I'm about to take it to the dealer. Any suggestions before I do that?

 

it sounds like you have covered a lot......I wonder if the MAF could be bad or maybe the ECT sensor..........have you done a detailed fuel pressure test because some of the symptoms sound like that.......I know you said you checked fuel pressure at the rail?...........any luck catching a pending code when it acts up?

 

Thanks for the feedback. I'm wondering about the MAF, too. Hate to just throw parts at it but might try a new one. I just checked fuel pressure at the rail and it was in the normal range. Haven't replaced the ECT sensor but will check into it. One thing that is odd is sometimes you can just tap the gas pedal and the engine will return to the normal idle speed for a few seconds. Also, when it bucks and jumps it doesn't sound like an engine misfire sounds but more like a fuel starvation miss or issue.

 

I bet if you purchased an "ultragauge" and drove around with it you would be able to diagnose it. I think they are about $70. I don't own one but have only heard great things about them. I am going to purchase one myself

 

Did you do a KOEO and a KOER fuel pressure test? How many cycles of the key did it take to get to full pressure @KOEO? After you shut the truck off does the pressure drop more than 8psi in 5 minutes?

 

One of the threads I read in another forum lead me to it possibly being a fuel issue and I did the fuel rail pressure test last summer. Can't remember the readings now but at the time engine on and off readings and pressure bleed off were normal and in the good range.

I'm going to check into the meter you mentioned and since I sort of have a feeling it is a fuel system issue or some faulty sensor related to the fuel system I need to re-do my fuel system tests. Again thanks for the feedback.

 

I've had the same problem with my 99 Ranger 4.0 for several weeks; very rough idle. Often runs rough after warming a few minutes then heading up the road. When I get up to speed then back off the throttle I get a really rough idle. Sounds like it actually wants to shut down at times. But it also idles very rough after warm up. Did get a friend to use his diagnostic tool a few weeks ago. Showed too lean a fuel mix. That's when I changed the fuel filter. That seemed to work for a few days then right back to where I was. Today I'm going to clean the MAF with the MAF cleaner and keep going form there. Keep us posted and I'll do the same.

 

I have a 93 ranger 4.0 with 240,000 miles on it and it runs great still although I have had a minor rough idle in the past. Since I've been told that the factory puts a coating on the throttle body to prevent build up The only cleaning I've done is using a rag with carb cleaner on it i've lightly cleaned the edge of the throttle plate and the housing where the throttle plate almost touches. this helped my problem with a slight rough idle as well as cleaning the MAF and air intake temp sensor. when I used to work in a shop up until 6 years ago I've seen a rough idle from a chunk of catalitic wedging sideways and causing a rough idle but it wouldn't run well either, let alone climb hills or accelerate. I've seen greasy, dirty crank sensors cause intermitent problems too since it tells the computer where TDC # 1 is, the RPM. It's not the most impotant sensor but without a clear signal it can cause ignition and fuel injector timing problems. Hopefully no one has changed the throttle stop setting, if so, the AIR may not be able to compensate properly. Another possibility is chaffed wires or corroded wire harness connections, espesially if it's intermittant.

 

You've been plenty busy on this one & may have more than one problem.

Suspect everything that hasn't proven itself.
Even though you say you don't have any trouble codes, I'd consider scanning the computer again for any pending codes, as there may some stored that haven't happened often enough to turn the CEL on yet & could offer up good trouble shooting clues.

As the engines sensors, actuators & computer need a stable electrical feed & with the mileage you have on this trooper, make sure the battery & alternator under load output is up to spec. Most autoparts stores will do an in vehicle electrical system check up at no cost, with their portable electrical system tester.

Once your certain the electrical feed is up to spec & stable, the IAC is responsable for maintaining proper engine idle speed, so make sure the electrical connector to it is in good shape, it's coil resistance is within range & that it's getting at least 10.5 volts to operate.
The IAC is either open or closed. The computer sends it a pulsed signal, whos on pulse width varies, to cause the IAC to be open more often when more air is needed (longer on pulse width) to idle the engine up, so if the IAC, it's electrical connections, wiring, or pulsed signal from the computer are corrupt, it'll act out & mess with engine idle speed.

I know you said the IAC is new, but that doesn't mean it's automatically good, I've seen bad new parts right of the box!!!!

With your multimeters leads properly connected, Red to + & black to - on the meter, disconnect the IAC electrical connector & place your multimeters + lead on the IAC's VPWR pin & the - lead on the IAC pin, it's coil resistance should read between 6-10 ohms. If you get the meters leads polarity reversed, it may read differently, because of a diode thats in series with the IAC coils windings.

Reconnect the IAC electrical connector & back probe with the meters + lead to the IAC's VPWR lead, the meters - lead to ground & you should have at least 10.0 volts to ground.
If the IAC resistance or operating pulsed voltage are out of tolerance, it'll have an operating problem.

If the computer's output, or it's wiring to the IAC are corrupt, it'll have a problem.

Same for MAF sensor & TPS electrical problems, so check those sensors, electrical connections, wiring & flex them when testing also, even though you don't have trouble codes for them.

With the mileage you have, the idea to pull & carefully clean the throttle body may not be a bad idea either as has been said, especially if you think the throttle plate may be dirty & sticking. Also as been said, be careful not to remove the coating inside the TB bore.

On my intermittent under load miss, the Dealer found a cracked external insulator on #6 spark plug, using the "wet down" test. You can do this with a spray bottle of water at night & wet down one plug & wire at a time, all the way back to the coil pack, while looking/listening for arcs & sparks or rougher idle. Make those new parts prove themselves!!!!!
Also the coil pack is known to crack underneath out of sight & electrically break down & cause mischief. Most autoparts stores can & will do a output bench test on the coilpack. Maybe take your spray bottle of water with you, for another wet down test, if need be.

On the bucking & acting out when coming to a stop, what happens if you shift to "N" when it begins to buck. I'm thinking maybe the torque converter may not be unlocking, so it would sorta be like stopping a straight drive without pushing the clutch in.

I like the KOEO, KOER & leak down fuel pressure retest idea, just to make sure Murphys Law isn't messing with you, since you measured it last year.
Make sure you don't have an intermittent voltage drop to the fuel pump. So maybe consider thumping & flexing the feed wires all the way from the power distribution box fuel pump relay, to the in cabin inertia switch, to the fuel tank electrical connector.

If you have the extra cab model, there is a TSB out, on an electrical harness chafing & feed problem, where the harness goes through the floor board, under the drivers seat.
Rockledge had a nice thread on it with pictures & I believe there is a link to it in the "Tech Info" thread atop this forum.

More thoughts for pondering, let us know how it goes.

 

Today i was on my way somewhere and my check engine light appeared. So i took it to advanced auto parts and they said its either the oxygen censor or a leak in cordinate 1. Just wondering what I should do? I have noticed after its warmed up it idles rough like doesnt stay the same idle. Just wondering what was wrong?? Any suggestions? Thanks by the way its a 1999 ford ranger v6 4L

 

Please post the actual code #'s........all of them?

 

Welcome to FTE.

Go to the thread listing page & start a New thread, so that you get responses just for your problem.
In the new thread post the trouble code Numbers found, along with the vehicles particulars/year, engine, tranny, cab type, mileage, where you are on all past & present due scheduled maintenance & if this problem came about after some event.

 

Ok got the codes P0171 and P0174. Not for sure what to check but he said its prob the 02 sensor since I got 100,000 on my truck.

 

P0171 means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.
Symptoms

You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.
Causes

A code P0171 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor.

Possible solutions include:

In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect all vacuum and PCV hoses, replace if necessary
Check for a dirty fuel filter and proper fuel pressure
I had same codes and I changed the MAF sensor, checked fuel system and still haven't fixed. Vacuum leak is what I am looking for now. I would clean the MAF sensor and if that doesn't work tap on the sensor after you reinstall it and if your engine idle changes while tapping on it you have a bad sensor. The solder inside the sensor can crack. Don't make same mistake I did and let the auto part salesman sell you the most probable cause. Could be something as cheap and easy as fuel filter, cleaning the sensor or just plugging in a vacuum hose that has come loose. My suggestion would be start small and cheap.

 

My son's '96 4 liter was blowing codes P0171 and P0174 during inspection in February, unfortunately the CEL does not work.. so it was a bit of a surprise. I had this past summer replaced the EGR and the tube from the EGR valve to the exhaust manifold. I took a bit of advise from another forum and sprayed carb cleaner on the vacuum lines, intake and finally the tube that runs from the intake to the EGR valve.. and the engine started to race... found something... started poking around with a screwdriver and poked through the rusted tube... FOUND the intake leak!!.. for now I sealed the tube with JB-weld and permatex and the truck passed with flying colors!!Does anyone know if I have to remove the intake to replace this tube? ot just unbolt from the EGR valve and pull it out of the intake?