1999 f150 with stalling issues

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Jan 31, 2012 | 09:24 PM

Mark DeDo

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1999 f150 with stalling issues

Hey there. I have a 1999 F150 4x4 with a 5.4L engine with 129k miles on it that has just started having issues with stalling. I have yet to have the codes read on it and will do so when and if I have time in the next couple of days but I wanted to see if anyone else out there has encountered any similiar problems. The truck idles fine in park but I noticed the other day when I was doing about 30 down a neighborhood street that the engine seemed to lurch like it was stalling then came back to life instantly. I then noticed later in the day that after I had accelerated from a stop sign and again reached a slower cruising speed that the truck stalled. Fired it back up and went on my way. I again left for work that night and was idling (with tranny in drive) at a stop light and the RPM's dropped then stalled again. Same thing in the morning when I left work but only this time I basically had to power brake it with RPM's up to get her home. I did a quick check for vacuum leaks this afternoon but was unable to locate any problem since truck idles fine in park. I was reading up on the EGR valve and regulator and it seems like it may be a problem but I haven't had the time to troubleshoot it yet. No Check Engine light has illuminated as of yet. Any advise would be appreciated. Thanks!

Jan 31, 2012 | 11:36 PM

Bluegrass 7

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No no.
The idle control is faulty.
Look at the IAC 'intake air controller' on top of the engine near the throttle body. It has an electrical connector.
On decell the PCM closes down the IAC and leaves itjust enough open to keep the engine from stalling.
It's stuck closed so idle and decell will be affected.
There's no code for this type fault.
Good luck.

Feb 1, 2012 | 12:08 AM

Mark DeDo

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Thanks for reply. I was thinking it may be the IAC but I changed it about 30k miles or so ago and it was a Ford part replacing the original. The symptoms I had then were RPM's all over the place while idling in park and drive. The truck now idles perfectly in park, it is only when I decel to an idle while in drive and low RPM driving. I'm going to take it off and check the resistances and so forth.

Feb 1, 2012 | 12:38 AM

Bluegrass 7

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If the idle is stable at about 750 in park or standing in gear, the trans speed sensor may be a problem.
The combination of TPS being at it's idle position and road speed coming downward in decell is how the PCM knows what is happening and responds with fuel cut down and IAC close down but only to the point the motor does not stall.
The Crank sensor keeps track of the RPM and provides corrections to allow the IAC to open/close as needed to keep the motor running.
Something in the chain is faulty.

Feb 2, 2012 | 12:48 PM

Mark DeDo

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Its is definitely not the IAC. I see the trans sensor but I cannot find the Crankshaft sensor. Is it under the intake? My Haynes manual dooes not show a picture for the 5.4 . It's weird because it idles fine and when I slowly accel from a stop sign it goes a couple of feet then shuts the engine down. It does not want to start back up right away either like it lost it's prime or something.