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78 T/A 400 Ideling at 3000rpm!!!!!

This is a discussion on 78 T/A 400 Ideling at 3000rpm!!!!! within the Classic Muscle forums, part of the Vehicle Specific category; So i have this 1978 Trans am with the 400 and 4 speed manual. Not long ago i switch out ...

  1. #1
    Member 10erg01's Avatar
    Join Date
    Nov 2009
    Columbia, Mo
    1998 Firebird Formula

    78 T/A 400 Ideling at 3000rpm!!!!!

    So i have this 1978 Trans am with the 400 and 4 speed manual. Not long ago i switch out the stock intake mainafold for a edlebrocker high preformance intake mainafold. when i got it all done and started it up, it was ideling at 3000rpm!!!! I know it has something to do with the carburator because i was not so sure when i put it back on if i put it on right. Most likly is it is a vaccum hose that i have hooked up wrong or the springs are in the wrong place.

    Picture of the carb as it is now, let me know if you would like better pics.

  2. #2
    Veteran Blackbird WS6's Avatar
    Join Date
    Jun 2008
    van down by the river
    i have a Edelbrock 1406 carb if you want? have some other parts as well

    but sounds like a vaccum leak and or make sure the cable is not binding up

  3. #3
    Super Moderator
    pajeff02's Avatar
    Join Date
    Feb 2009
    Mansfield, PA

    Black & Blue
    '02 WS.6 / '07 Suburban

    Either a vacuum leak or you're way out of adjustment on your stops. With the engine off, push the choke plate open and look down the primaries. The throttle plates should be almost fully closed. If not, take a look at your idle stop screw on the driver side of your carb below the linkage. If this looks ok, then check you choke settings on the passenger side. There is a stepped cam that forces the primaries open when the choke is engaged. You should be able to manually set the choke and see the effect on your throttle blade angle by looking down the primaries. If everything looks good, then start the car and see if anything moves or hangs up that would cause the throttle to be held open. Manually disengage the choke and see if it'll idle down. If everything checks out on the carb, start looking for vacuum leaks. Is the brake vacuum source attached to the port at the rear of the carb? Are any unused vacuum ports capped? Is the carb snugged down on its gasket (not too tight!)? After these checks, you are down to the intake manifold being the issue and maybe a gasket slipped or got knocked out of place.

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