Rough idle, rich exhaust but clears with higher RPM

Discussion in '4.0 Engine' started by HotRodFord, Apr 4, 2014.

  1. HotRodFord

    HotRodFord New Member

    Hey gang! Im kinda stumped with this one... My 1994 4.0 5spd idles very rough on start up almost to the point of dying, however running the RPMs up will clear the rough idle and check engine light. The problem will also come up randomly when driving, usually in 3rd or 4th gear, but will again clear when engine is revved up.

    I have replaced:
    Mass air flow sensor
    IAC valve
    Plugs (autolite)
    air filter
    and cleaned the throttle body

    also checked all injectors and spark at all 6 plugs.
    my truck does not have an EGR.

    I have heard the TPS could be the culprit, also maybe a cracked upper intake which I will test after this post.

    For what its worth I work out of town and the truck has been sitting for 5 days of the week until I come back on weekends, and the problem first came up after sitting like this for a few weeks.

    Any help is greatly appreciated!
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  3. RangerAl

    RangerAl Member

    You didn't mention Oxygen sensor, I am not a big fan of Autolite. MOTORCRAFT when come to spark.

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