My 1997 F150 4x4 with a 4.6 v-8 has an ongoing problem which dealers have thus far been unable to diagnose. I first noticed it at 30,000 miles or so just after I bought it used in December 1996. When I have the truck in gear (automatic tranny) and come to a stop, the idle goes down into the 3-500 range and the engine runs very rough. If I take the truck out of gear, sometimes it will idle back up and is fine. Lately though the problem seems to be getting worse. It does not always quit until I rev the engine and take it out of gear. Every dealer I have been to just wants to hook it up on the computer and it never gives any codes. Any suggestions?

 

Rad,

There was a thread a while back regarding a wiring harness being too close to the air conditioning system's receiver/dryer causing some drivability problems like you mention, but that was supposedly on a 5.4 liter. The thinking is that the metal of the cylindrically shaped dryer interferes with the electromotive waves that always surround any wire under load, and by moving the harness just a little way and securing it, the drivability problems disappear.

However, I have a '98 4.6, and I also found the wiring harness awfully close to the receiver/dryer, which is located adjacent to the battery on the passenger side of the firewall in the engine compartment. You might check your harness and if it's close to the cylinder, move it and strap it out of the way, just for grins if nothing else.

If it clears up your problem, that would be the first case of it being related to a 4.6 engine that I know of. It would also make me feel awesome that maybe I figgered it out and the Ford techies didn't, so go ahead, make my day!

 

Did the dealer say "there are no codes, so NPF"? Does this occur with the A/C on or off?

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'98 4.6 5-sp F-150
We've come for your Tundra.

http://www.mcmullenargus.com/gallery...ge=1165&pub=12
trixters-playground@excite.com
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[This message has been edited by crash1 (edited 12-03-1999).]

 

RAD2
I have the same exact problem with idle that you have only my engine is the 5.4l.
I have moved the wire harness and it never did anything! The only other thing i have done though is sprayed the mass air flow sensor with carb cleaner so that it would give the computer a colder temp signal and it idled perfect.HMMM, Then it started back again after the temp between the two sensors equalized. My situation is probably a little differnet but i've had it into the dealer so they could tell me this this is normal because there were no codes. BULL! My new piston slap free 2000 engine ran beautiful for about two weeks then this idle crap started. Is your idle problem more noticeable when it's first started? Mine is really noticed when you first start it, let fast idle drop down to say 900 rpm then put it in park and the rpm will drop and bounce a few times until the computer bumps the rmps up to a steady 650 or so. It definately is felt in the drivers seat. Once the computer corrects itself it is not as bad but it still misses? Let me know if you find anything out!
I think it is going to come down to a dealer that takes a snap shot reading of all the sensor values while its running and then analyzes what is actully going on! These computers don't flag everything if it can correct them! Technology is great but it can be a pain also

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1999 F-150 4X4 Super cab lariat, 5.4, 3.73 gears,deepwedgewood blue,
and all the options, build date 3/1/99

 

Hey guys-my brother in law has a '98 4.6L with that same problem.He said it would idle down real low at stop signs and red lights.I don't believe it ever cut off or anything but made him think it might sooner or later.Local dealer first said it was something to do with manifold pressure but upon further investigation they decided he needed a transmission rebuild.He only has 34000 miles on his truck(almost all of it highway miles). I'll let you know when he gets it back if the problem is gone or not.Also I want to know what failed in his tranny so soon.

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1997 Black F150 SC Flareside,4x2,5.4L,3.55 LS,tow package,appearance package,captain's chairs,tinted windows(darn silver flipout windows!),Flowmaster catback with 40 series,painted to match slotted taillight covers,vent visors on front doors only,K&N,Hypertech module and Rhino liner(was black-now gray)
Protected since new by Desert Eagle .50 cal.

Future mods:buying a house come first of the year!

 

I haven't had a chance to try moving the wiring harness yet but the message by KnightS makes me nervous. I had some trouble with the tranny early on and they replaced the valve body (I think that's the right name for it - anyway the part which controls the shifting of the auto transmission). It actually seemed to help the truck briefly but the same problems came back. I have wondered if my engine problem has something to do with the vacuum system. I know the vacuum gives power to the brakes and also contributes the force behind the transmission shift (I guess I should say I think that's how it goes as I am definitely a change the oil/fluids /brakes type when it comes to working on my cars). I wondered if the tranny was somehow hanging on to its share of the vacuum pressure or something to that effect which, coupled with the draw on the system from the brakes might be collapsing a vacuum line which helps control engine idle speed (though I am led to understand this is all controlled by the computer). Does this sound too far-fetched?

 

I have the same problem with 99 4.6, except my trucks a 5-speed!!!! ALSO, i have had it stall on me in parking lots and on the highway if i put in the clutch. Its been to the dealer 5-6 times and they have no idea what they are doin. They have replaced the 02 sensors like 3 times, and nothing.
ANyone have any suggestions about getting new engine\truck? (though i dont know how i could part with my BABY after all we have been through!)

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1999 Black F150 XLT Sport 4x4
Flareside
4.6 Triton V-8
Manual Transmission
Captains Chairs
Button-down Tonneau Cover
Webasto Sunroof
Spray-on Bed-liner
Superwhite Bulbs
Blackwidow Car Alarm

 

THEY FIXED IT, thank god, would have hate to have lost my TRUCK!

Something about replacing a "modular" or something!?!?!?!?

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1999 Black F150 XLT Sport 4x4
Flareside
4.6 Triton V-8
Manual Transmission
Captains Chairs
Button-down Tonneau Cover
Webasto Sunroof
Spray-on Bed-liner
Xenon Fog and Headlights
Blackwidow Car Alarm

 

Could it be modulator?
The IAC modulator is what controls the idle air bypass to the motor to control idle speed. It lets air bypass the throttle body. If you have an older motor, or running a K&N filter, there is also a bypass port in the TB. It is a needle valve that has a hole near the throttle plate and it exits behind the plate. The needle valve gets crusty buildup that reduces closed throttle airflow that causes the IAC modulator to hunt around for the right speed.

Birdman

 

I have this same problem with my '97 4.6 auto. My exhaust also smells like rotten eggs, which is usually an oxygen sensor. I am going to be taking mine in soon to get it looked at and hopfully fixed.
I had a '97 4.2 V-6 with 5-sp. I had problems with it idling bad and even stalling at stops. I even had it stall on me and ended up in an accident. Got T-boned causing $3000+ damage. So after I got it back from body I traded it in on other truck.
Insurance company won't go after Ford stating that it was because of my K&N filter or because of my aftermarket alarm. Well the alarm was completely out for a month and a half and it still did it. I also took out the K&N and replaced it with factory and it stalled even worse after that. I'm getting the run around from ins. comp. and Ford wouldn't fix the prob. Hope this truck isn't starting the same thing.

 

yah i believe it was the modulator.

thats horible red97, but i believe that ford can only refuse to repair a truck under warranty if they can prove that, say the k&N, caused the problem

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1999 Black F150 XLT Sport 4x4
Flareside
4.6 Triton V-8
Manual Transmission
Captains Chairs
Button-down Tonneau Cover
Webasto Sunroof
Spray-on Bed-liner
Xenon Fog and Headlights
Blackwidow Car Alarm

 

I have very similar symptoms on my '97 4.2.
Could it be the modulator also?

 

Rotton eggs is usually a bad catalytic converter. The material inside breaks down and gives you the sulphur smell.

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1997 F-150, 4.6, automatic, Dark Toreador Red, Supercab, Flareside, 4X4 Off-Road, Towing Package, Ford hvy dty rubber floor mats, Kenwood 10-disk cd changer, Kenwood am/fm cassette head unit, Ford bugshield, Chrome Grizzly Wrap Around Push Bar with 2 KC 100w Daylighters, Lund Lunar Visor, Ventshades, Ford bedliner, Lund Premier tonneau cover, cab and bed professionally undercoated, Code Alarm Sure Start RVS remote starter, Ford alarm, Realistic CB with Wilson Little Wil antenna, ported MAF sensor, and Lots of TLC!! (Besides being an F-150 nut, I am a Ford auto technician.)

 

Sycoholic: My parents had a '97 F-150 and the sulfur smell was cured with a new oxygen sensor.
Coolsvile:Ford didn't refuse to fix it, they just couldn't fix it. They were stumped.

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Red '97 F-150 SC 4x4 off-road, 16" rims instead of 17"'s, BFG all terrain T/A, K&N filter, Expedition console, 3" rear seat lift, after market stereo seen at HTTP://members.sounddomain.com/red97, possibly putting on dual exhaust and putting in chip.

 

red97:
they were stumped for me aswell, so they then decided to put in a data recorder, all i had to do was push the button when the low idling occured, they then read the info and figured out it was the modulator.
if they havent tried this for u yet, u should ask about it. my truck had been in there about 8 times prior to the recorder with no luck. once they put it in, they figured it out within a couple of days

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1999 Black F150 XLT Sport 4x4
Flareside
4.6 Triton V-8
Manual Transmission
Captains Chairs
Button-down Tonneau Cover
Webasto Sunroof
Spray-on Bed-liner
Xenon Fog and Headlights
Blackwidow Car Alarm