I own a 2006 Ford Expedition. I just had the coil packs and plugs changed?
After having them changed, when the truck gets warm. The idle drops down to 250 rpm's and it dies when slowing down to a stop or turning. Can't find any vacuum leak and double checked all electrical connections. Any advice on what it could be?
Idle only drops with engine warm? Did you test for vacuum leaks with engine fully warmed up? Could still be a vacuum leak from a vapor management valve/circuit which only applies at warm engine… The VMV allows the engine to draw vapors from the charcoal cannister when the engine is warmed up… If there's a problem with it, it could lead to a vacuum leak of unmetered air and cause stalling… Try pinching off related vacuum hoses with a vicegrips near the vacuum source and see if it helps idle when warm… If so, inspect vacuum lines to VMV and for bad VMV/circuit. Or pinch off various hoses near the vacuum sources/manifold ports and test idle speeds with warm engine The PCV tube and vacuum line behind TB and under the intake are common issues to check… Hard to get at to test properly and could be missed. Any chance changing plugs affected a nearby vacuum hose? Ricks advice is a good idea as well although a bad booster diaphram /vacuum leak would likely occur at all engine temps. What you need to pinpoint is areas that could have issues when the engine is warmed up if that is the case. Some electrical devices as well may work well when cold but can fail when warmed up due to high internal resistance issues.
Possibly a bad throttle body which may need cleaning or testing… The TB has a computer controlled stepper motor which controls throttle blade position for idle speeds rather than an IAC used on earlier models… Those later models did have a lot of problems with bad TB's… See link below…
http://www.justanswer.com/ford/20ed8-change-iac-valve-2006-ford-f150.html
Related info on stalling…
http://www.fordforums.com/f60/2003-expedition-5-4l-rough-idles-stalls-134357/
VMV issues…
Test: With the engine running & the truck just sitting in PARK, step on the brakes. IF the idle gets rough & lumpy just when the brakes are on, check the vacuum booster on the power brakes for a leaking diaphragm.
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