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1998 Ford F-150 Question: Rough isle. runs fine at highway speed, good acceleration.

 

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schoon12, 5.4L V8, Townsend, GA, February 13, 2014, 20:00
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It idles at about 800-900 rpm smoothly, after about 10 seconds, something changes and the rpms drop to about 550 rpm and very very rough. Very rarely will it die. It appears that the computer is telling something to open or close making it idle rough. Can not find ant vacuum leaks. Could the EGR or the idle air valve cause this?
Thank you.

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  • Answer #1

    pushrod February 13, 2014, 20:48
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     Master

    Have it scanned for codes and so live data can be viewed.

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    Greg's Orange Auto (12847 Answers) , Orange, CA - (714) 361-9386
    globalhelper February 14, 2014, 06:34
     Master

    egr could be stuck open causing vac leak

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    schoon12, February 17, 2014, 20:18
     Rookie

    This is something I will check. RPM decreases to about 800 on deceleration, will hold this for about 10 seconds than something gets a signal and the RPM drops to about 550 and very rough idle. Very seldom does it die. Thanks for the input, will check EGR value.

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