I have been having a problem with a 98 Ford F150 4.6 liter..
After cleaning the throttle plate area (While it was still assembled on the motor) the truck has a high idle. It seems many of you had this problem..I've performed the relearn process..etc..and still can't get the idle down
The owner had told me that he had the same problem regarding the idle after having the fuel injection serviced by the dealer...After driving for about 2 weeks the idle returned back to normal...

Can anyone offer a solution???? I really don't know where to go next...
Thanks to all!!

 

Vacuum leak or the IAC.

Steve

 

Check the PCV hose behind the throttle body at the elbow and see if it is sucking air! Common problem on all F series with the 4.6. The new PCV hose is less than thirty bucks from the dealer. Even comes with a new valve.

Robbie

 

yea i did the whole throttle body cleaning and put a new battery in last weekend and my 4.6 runs like a scalded dog, but idles high
Guess ill check all the hoses for leaks,etc.

 

Here's what happened when I checked the truck last...

I checked for vacuum leaks(pcv hose, base gasket..etc) ..this all checked out OK..I then peceeded to do the relearn process by diconnecting the neg. cable turning on the headlight switch...and so on...The idle did come down and it seemed to run well..
However..

Later that day while driving, the rpm raised up again and the same problem is still there!!!

The IAC has been changed..But I still get a check engine light with a code po1506...IAC overspeed problem...using the test procedure in the troubleshooter...It was narrowed down to a defective IAC...As you can tell this did not correct the problem

Any thoughts on what to do Next???

 

The first thing to look for are vacume leaks, pcv, lines going under battery tray, posable leaks between mass air and throtle body, plastic intake, start engine and listen closely you will have to visualy inspect tube from mass air to throtle body,
while ideling disconect conector from IAC see if this changes idle also can be leak to evap valve or bad evap valve located by booster on fire wall this should also hold vacuem. You can eletricaly check the IAC should be 6to 13ohms between the two terminals and 10000 ohms or mor from ground to each of the terminals.
As a last chance to elimanate the IAC you can remove it and block off the pasages if it is IAC related it will idle down also beshure the throtle plate is closing all the way and that the TPS is not bad or sticking.
Hope some of this helps