My 99 F150 4.6L with Manual transmission has had an idle problem since about 8000 miles,it now has 24000. I will be stopped at a traffic light , for example, it will be idling normally and then without any apparent reason the idle speed will drop and then immediately recover. I have had it at the dealer 2 times for this so far and they can't find anything wrong. This is especially dangerous when turning into a parking place, etc., and you lose power, then you momentarily lose power steering and power brakes. It doesn't matter whether the AC is on or not and it was doing this before I had dual exhaust installed.
Any ideas??


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

[This message has been edited by LTDC (edited 11-12-1999).]

 

check out the spark plug wire threads. could be water in the boots corroding the terminals. That problem will not show up on the scope when you take it in. I have a 99 4.6 that idles perfect.

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'99 XLT S/C 4.6Romeo, Auto, 3.55 LS, Oxford White, Dark Graphite int., Tow Package, Orlando appearance package (Body color honeycomb grill, mirrors, and Lariat wheels)

98 Explorer XLT SOHC 4.0 V-6, moonroof, 3in1 Stereo, leather

71 GMC 350 4bbl. automatic, PS, uplevel trim

89 Dodge Van fancy steering wheel cover, radio doesn't work

 

Could be the O2 sensors...i had a similar problem on my '97 F150 and one of those had to be replaced.

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1999 F250 SuperDuty, XLT, PSD, supercab, shortbox, 4X4offroad, 3.73 limitedslip, 4R100 with PTO, Grey Rhino-liner, Retrax retractible hardtop, GVWR=8800, TC=13800, Lariat wheels, 295/75/16 BFG AT, power TT mirrors, Clarion CD/EQ/DSP, soundstream/PPI amps, JL/Boston speakers, and...

 

Try another dealership, it is under warranty, they should fix it.

 

Mine did that once at about 30K miles. Never coded out and never did it again. At 45K now and running good so you got me what it could be. Try resetting your computer buy disconnecting the battery for an hour and see what happens. There was some discussion of idling problems on 99/00's that resulted in reflashing the computer with a later code to solve. But I think tah was on a 5.4L There might be a TSB on that? Anyone?
And, yes have them check those plugs and wires as well just in case. The probelm was in a 97 but you never know.

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97 F-150 SC Lariat, Styleside, White over Gold, 4.6L (Windsor), Automatic, 3.55 rear end, electronic 4X4, w/ every option of Lariat and ORP packages except the 17" wheels and the 4X4 decals, MODs so far: K&N air box mod, Gibson Super Truck, clear Bugflector II, Leer TSC 600 hard cover, Bridgestone Dueler OWL ATP 265/75 R-16's, TrailMaster Invader N7 shocks, Smittybilt step bars, Ford moulded mud guards, "White-white" head lamps, Bosch platinum + 4's.

 

When I first got my 98 F150 It did this as well. I had the same symptom where it will be idling normally and then without any apparent reason the idle speed will drop and then immediately recover. It would only stall during the warm up cycle say 5 to 10 minutes after a cold start at about 40 degrees F. The dealer found a TSB that had to do with a vacuum line from the fuel tank get caught between the frame and the box during the assembly. They lifted my box move the pinched line and the truck has run great since. I would have thought that they would have fixed the assembly proceedure for the 99's though but you may want to check this anyway.

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98 F150 XLT SC 139" WB 4.6L Automatic 3.55 Rearend Tow Package Toreador Red /Tan 5 Star Lariet Style 16" Wheels 255/70/16 OWL Goodyear AP Tires
Mods K&N Filter, Ranch SportLid Fiberglass Toneau
Tow 22" Terry Taurus