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  #1  
Old 08-14-2003, 09:13 AM
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Location: Biloxi, MS
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Unhappy 4.6L Rough Idle

o.k. guys, i need some input. i have a '97 f150 SC 4x4. My truck is idling rough, but it only does it maybe once a day. When i come to a stop, and the truck is hot, the rpm's start dropping to 500 or less, and the truck starts to act like it wants to die. its actually never died. if i give it some gas, it will start sputtering, and finally take off. it also tends to do this more when i'm towing a load. the truck has 105k on it. Here's what i've done so far:
1. New plugs and plug wires
2. new fuel filter (its in the correct direction)
3. new pcv valve
4. new IAC valve

The biggest problem is that i can't get the truck to repeat the problem in the drive way. i would love to be able to pull the spark plug boots to check for a misfire. It set a light about 6 months ago, but it went out shortly after that. will the code still be saved? the light has not came back on. any ideas? i hate to keep putting money in parts that don't need to be changed. i'm thinking: DFPE, EGR, Coil Packs, MAF, and maybe the Fuel Pump. any ideas would be greatly appreciated.
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  #2  
Old 08-14-2003, 05:32 PM
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I would look at the EGR system.
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  #3  
Old 08-15-2003, 10:25 AM
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if you don't mind, let us know what the problem was with the rough idle....i think i have a similar but less severe problem for now.......thanks
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  #4  
Old 08-15-2003, 12:47 PM
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good luck...

I've given up on finding out the cause of the rough idle. After reading this board (and others), it would appear no one really knows. I'm afraid I would do the same thing you did...throw $$$ at it and never fix the problem, tho I am due for a plug/wire change.
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Old 08-15-2003, 01:05 PM
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Location: Sorrento, Fl
Vehicle: 1999 Ford F150
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rough Idle

I have a 1999 4.6L with 82k miles. I've had a similar problem. If I run the truck hard on the highway at high speeds, then get off into traffic, at the first stop light it will cough and sputter and you'd swear it was going to stall. It never has but it makes you wonder. It is much much worse with the a/c off.

Sad to report, it's done it since it was new. It doesn't do it in light driving... ie, the dealer can't reproduce it, so they've been useless in solving this problem. Running the a/c seems to help, I think because it causes the engine to run a little faster.

Art
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  #6  
Old 08-17-2003, 03:40 PM
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My truck has stalled out 2 times in the last year its a 2000 and a 4.6 both time it staleed was going up a slight hill making a right turn.
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  #7  
Old 08-18-2003, 07:46 AM
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well, a mild rough idle is one thing, but the almost stalling is making me nervous. i went ahead and got a new DFPE sensor. I installed it yesterday. will let you guys know if any improvements. its currently hitting 95 degrees here on the Mississippi Gulf Coast, so i'm sure, if the problem isn't corrected, i'll know soon. i have to run to Mobile today, so it should be a good test.

If this doesn't work, then i'm changing the EGR valve, and EGR Vacuum Solenoid. Also probable put in a new MAF. Does anyone know how long the EGR Solenoid typically last in these trucks? also gonna clean the passages in the throttle body.
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  #8  
Old 08-18-2003, 09:14 AM
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After a lot of time with my truck and finding this to be the problem I would suggest. Starting the truck when the engine is warm . From underneath look at the lower side of the heads. Look for carbon tracking below a cylinder and or oil bubbling out.


tom
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  #9  
Old 08-18-2003, 11:40 AM
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Almost dying out at stop light after high speed driving...

This has happened to me ('97 F-150 4.6L) as well. Especially after a rapid decelleration from 80mph, the engine idle goes down below normal and it feels like the engine is dying, but then it recovers to normal idle.
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  #10  
Old 08-18-2003, 12:03 PM
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maybe someone can tell answer this. if the EGR valve is opened at idle, would this cause the engine to bog down and act like it is going to die? The EGR only opens when the engine is running fast correct?
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  #11  
Old 08-18-2003, 01:08 PM
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Unless the code was manually deleted with an OBD-II scanner, it should still be there. Few months back, I had a check engine light come on, then off, then constant on again. My truck had a similar symptom, somewhat of a rough idle and low around 600 rpm. I checked the code with an OBD-II scanner. It showed up as a faulty O2 sensor, downstream right-bank, code PO141 if I remember correctly. I replaced only that faulty O2 sensor. Check engine light eventually went out after driving it a few hours, but I had to manually go back and delete the code or else it won't pass the smog test (the smog stations in California can read the error codes). The rough idle went away after about a week. I had 45K miles on my '97 4.6 S-Cab 4x4 at that time.
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  #12  
Old 08-19-2003, 08:54 AM
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well, after i installed the new DPFE, i unhooked the battery and turned my headlights on to reset the PCM. do you think the code is still there or erased? Autozone told me they could only pull the code if the light was on. Is this correct? the light will not come back on. I drove to Mobile yesterday, and the truck started idling rough again. the RPM's never dropped to the low 450 or 500 range, but it did go down to about 600. that made the truck shake pretty good. I'm going to focus on the EGR system. i'm gonna take off the TB and clean the EGR inlets, and the EGR valve, also may replace the EVR solenoid. If i can get the code read, this would be a big help. It may very well be the O2 sensor, so i need this code. all the vacuum lines seem fine and in working order. like i said before, it only does this when the truck is hot and at a complete stop, and it will only do this at about once in every 20 stops. if the truck is in park or neutral, it idles just fine, no matter how warm the engine is. any more advice will be greatly appreciated. thanks for all the help so far.
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  #13  
Old 08-20-2003, 05:43 PM
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i had the same problem and i replaced my iac valve and it fixed it right up.
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  #14  
Old 08-24-2003, 05:16 PM
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need some advice. i'll restate what i've done so far:
1. new IAC valve
2. new pcv valve
3. new DPFE sensor
4. new plugs and wires
5. new fuel filter
6. remove throttle body and throttle body neck and cleaned.

the EGR is functioning, no vacum leaks, the throttle body neck was clogged severly, but i've clean it and the EGR valve. tested the EVR solenoid and TPS sensor, and they both have suffiecient voltage, according to the Haynes Manual.

after i cleaned the throttle body neck, the rpms went up to around 1000 to 900. the truck will not set a code, but when the truck is warm(after a good highway run) it will start idling rough, at the 1st or second stop, like it wants to die. the rpm's get to around 450, and it shakes bad. hasn't died yet, but acts like it wants to. does anyone have any other ideas, i could try? i hate to bring it in to the dealer. the truck has 105k on it. i wish it would set a code..
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Old 08-24-2003, 05:16 PM


 
 
 
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