My 350 is stuck at a high idle and will not go down.

Discussion in 'Engine Topic' started by Crowsville, Feb 10, 2013.

  1. Crowsville

    Crowsville Member

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    I recently installed an edelbrock 1406 with an adapter plate onto my stock 350 motor. The qjet in the past needed rebuilding and I found a place that sells carburetors with a lifetime warranty, which is what drew me into getting the 1406. The previous carburetor was also stuck in a high idle.

    I did the replacement today and everything went smoothly. When I went to start the car, it started right up with a high idle which is what I expected to happen being that I haven't adjusted it yet. 20 minutes roll by and it is still stuck at this high idle, I adjusted the idle mixture screws and even the screw that controls the carburetors idle speed when it is warm on the 1406 and it did absolutely nothing. Some wires that I had near my headers even burned off, it is just a nasty situation.

    Does anyone have any idea what could be the cause of this, because I am truly lost on this one.... I did a full tuneup minus the pcv valve and this is still happening... I also blocked off the EGR valve with an egr valve block off plate being that the edelbrock 1406 cannot fit with an EGR valve. Can someone please help?
     
    Last edited: Feb 10, 2013
  2. zekefreak

    zekefreak Veteran Member Lifetime Gold Member

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    Assuming you adjusted the idle screw I would make sure the throttle cable or the gas pedal isn't hanging up somewhere since you've had the problem with 2 different carbs. Try removing the throttle linkage and see if the idle goes down. If it doesn't then you have a problem with the carb and/or intake.
     
    Last edited: Feb 10, 2013
  3. Crowsville

    Crowsville Member

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    Good advice, thank you. I will check this out tomorrow. Process of elimination always works best.
     
  4. david.rosol

    david.rosol Veteran Member

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    Sounds to me the fast idle adjustment screw needs adjusted... on the 1406's there's an idle speed screw (on the driver side) and the "fast idle speed screw" (on the "pax side")... it's kind of in a wierd spot to get to and can only be accessed with the throttle fully open (motor off of course). Do a google search for "edelbrock 1406 fast idle adjustment" and a lot of stuff will pop up to show you how to get to it... basically, it has to be done with the motor cold... then back it off a full turn and then see if it works... if not maybe another turn more but that sounds like the issue.
     
  5. Crowsville

    Crowsville Member

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    David, I just googled it and there was a forum in the mustang forums. The owner of the 65 mustang also had a 1406, but his idle goes down after warming up, my idle doesn't even do that. It remains high no matter way I do.... At this point in time it doesn't hurt to give it a shot though.
     
  6. tmv36830

    tmv36830 Veteran Member Lifetime Gold Member

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    Make sure you do not have a busted diaphram inside the brake booster. This could cause a high idle also. Infact, any vacuum leak could cause a high idle.
     
  7. david.carlton@s

    [email protected] Veteran Member

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    I had the same problem with a new Holley. i had a major vacuum leak as discussed above.
     
  8. david.rosol

    david.rosol Veteran Member

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    Dang, my bad... I got confused with my Holley Carbs :screwup: ... the fast Idle screw is located on the driver side not the pax side as I mentioned previously under the idle speed screw... but you still have to open full throttle to get to it and adjust when the motor is cold. Yes, it's supposed to go down after it warms up... but if that fast idle screw isn't adjusted right... well, there is a lever that the fast idle screw controls along with the choke... and if it's out of adjustment, won't allow the choke to work the lever up as it should to allow the rpm's to drop when warm. This video points out both idle screws... http://www.youtube.com/watch?v=LtcBAUHJJBM
    Also, tmv36830did mention about checking for vacuum leaks... as you were having this issue on the previous carb as well... one common leak people don't check for is an intake leak - particularly in the areas where the intake contacts the block either in the front or rear of the intake, or even both. This can also cause your symptoms.
     
  9. Crowsville

    Crowsville Member

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    I took the throttle cable off the carburetor, no difference. I removed the pcv hose and plugged it with my finger from the pcv valve... little to no difference. I loosened the cold idle screw when the car was cold and it made no difference. When I looked at some openings however I thought maybe if I can describe what the part is someone can identify it and determine if it could be the cause of this really, really high idle.

    Towards the front right of the motor, near the headlights there are 4 openings that sit on top of this about 7 inch tall circular top surface part. One opening has a hose that sits on a line and if I am not mistaken reads the words fuel. Out of the four there are only one opening taken and it's by the hose I just described. I capped the other 3 off and it made no difference, maybe there needs to be actual hoses there that belong on key components?

    On the firewall, towards the left, if you're facing the motor there's something there that looks like a ball. This part has two hoses, the one on the top is thin and the one on the bottom is thicker. The one on the top of this part seems to be burned/cut off... can this be a cause of a high idle as well?

    I also found two parts on the intake manifold that have like 3-4 openings each and are about 2-3 inches tall they are near the thermostat/upper radiator hose and they just sit there. Seemingly serving no purpose or am I wrong?
     
    Last edited: Feb 12, 2013
  10. larrylarry

    larrylarry Veteran Member

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    You have a vaccum leak. The round can by the right head light is the charcoal can for fuel vapors. I would either take it out if you don't have to have it inspected or replace all of that vaccum line with new. The other ball shaped thing is a vaccum reserve I think for the a/c. Either shag it or put new vac. line on it. The carb. won't idle down because air is being suck into the intake man. some where. Also get a new thermostat housing without any of those vac. ports. Those vac. ports operated the heat thing that let heat into the air filter housing. If it were me I would shag as much vac. hose as possible. Check the hose going to the booster also. I only have 3. lines,one for the brake booster & one for the pvc and one for the vaccum advance.
     
    Last edited: Feb 12, 2013

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