From time to time, when i stop at the lights, the engine drops about 2-400 rpm's and pops back up to a normal idle.

why does this happen,
what can i do?

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1999 Black XLT Sport 4x4
Standard transmission, flareside, 4.8 litre triton

 

Don't know but sometimes mine surges drastically sometimes it just about dies and then revs up to 2200 or so then pops down and just about quits again until I hit the gas. Just does it when the engine is cold.

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99 F-150 XLT Sport, Black 4x4 4.6L , 3.55 LS,Manual Tranny, K&N air filter, No Muff Exaust system,.999 tuned TPS,Pioneer CD Player,Pioneer GM-X332 Amp,8" Rockford Fosgate Punches, Custom(self done)pinstriping,Wrap around bugdeflecter

 

mine does it all the time though, hot or cold

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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

 

My 5.4 used to drop from it's normal ~650 or so down to about 500 or 550 and run a little rough at stop lites but only every few stops for awhile last winter. Had about 2k to 3k miles on it then, but spring arrived and it does not do it anymore. I did switch to Mobil 1 around that time but don't think that would have cured it. Probably an ambient temperature thing.

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2000 Lariat, 5.4, 3:55 L.S., 4wd, ext cab, Tow pkg, Chestnut/Gold, Century mid-hi cap, Ford short bug deflector, contoured Ford running boards and bedmat.

 

Well, took it to ford AGAIN, and they fixed it, they had to replace a "modular" or something!

Glad to have my baby running back to normal

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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

 

Hi, Coolsvile....
It's great they fixed it first time, especially being a 'sometimes' type of problem! In case it happens to me again next winter, can you see if you can figure out what exactly they changed from looking at your slip? I'd like to have it for reference in case I need it.

Thanks a lot in advance...

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2000 Lariat, 5.4, 3:55 L.S., 4wd, ext cab, Tow pkg, Chestnut/Gold, Century mid-hi cap, Ford short bug deflector, contoured Ford running boards and bedmat.

 

I believe the slip is at work, so i try to find it, or if i have to, i'll ask them next time i go in for a check, so i'll get back to you on the prob.

 

Mine has done the idle drop thing on 2 occassions. Both times it was fixed by using a can of Techron in the tank and a whole can of air intake cleaner down its throat (per the directions.) This occured at about 46K miles and again at 53K miles. Might be worth a shot if you're experiencing this problem. It's a lot cheaper than a trip to the dealer for those of us beyond our warranties.

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97 F150 Lariat 4X4 Ext. Cab. 5.4, AT, Tow Pkg, bedliner, white/grey 2tone w/ grey leather, Fact. CD changer, Gibson Side Swept, K&N, Bosch Platinum +4's,Michelin LTX 265/70 16, S/D Triton V8 emblems, Both doors cracked, Piston slap quieted by Mobile One & Slick 50 Synthetic.

 

My 99 model 4.6L has been having this idle problem since about 8k. I now have over 36k and have had it at the dealer at least 3 times and they have not been able to find a problem. I made it stop doing the idle drop and bounce back for a period of about 10k by disconnecting the battery for about 30 minutes and then driving the #$^% out of it but it is doing it again and now I am out of warranty.

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LTDC
99 F-150, ext cab, 4.6L, 3.55 gears, limited slip, manual trans. catbac exhaust