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  1. #1

    Default 83 5.0 carbed stuck at high idle

    '83 5.0 w 4180 carb won't idle keeps winding up to about 2000+ RPMs. Last night, car was running and idling fine, downshifted to 4th on entering highway opened it up a bit then shifted to overdrive, all fine didn't notice anything. Exiting highway 10 miles later engine wanted to rev up to 2000+ RPMs. Timed most of the lights right and made it home but can't get rid of or figure out why the high idle? Checked this morning everything looks normal but still goes straight to high RPMs. Car does have A/C but is not working and is off.
    A little history, car had been sitting for several years before i bought it Oct. '17. Since October I have driven it very little less than 200 miles mostly just to locate the next problem. Seller claims carb was rebuilt shortly before sale. First thing I replaced was a leaking crossover tube and attached thermactor valve. Next was front end rebuild, ball joints, struts, replaced floppy tilt steering column. Then new radiator all hoses and 160*thermostat. Lastly, just 2 weeks ago, removed howling 3.08 7.5 replaced with 2.73 8.5.
    Have been test driving for right at 200 miles getting 15 MPG city highway mix, after 20% adjutment. Car was running great! Was planning on starting on the interior. Now this!
    Engine has all smog equipment however not sure if all is funtioning properly.
    Have to head out now but will check back in a few hours, Any ideas on where to begin will be appreciated.

  2. #2
    FEP Senior Member
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    Is your fast idle cam stuck or staying engaged?

    Another thing to look at is the throttle linkage for sticking and/or binding.
    Last edited by KevinVarnes; 07-18-2018 at 03:11 PM.
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  3. #3
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    I had a similar problem with my 83. Sticky secondaries, had to manually jiggle the shaft. Sold the car (stupid) before I got a permanent fix.

  4. #4
    FEP Super Member mmb617's Avatar
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    When I had a similar problem it was a vacuum leak at the intake manifold gasket. Drove me nuts for a while because I thought it had to be the carb.
    408/T5/3.73's

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  5. #5
    FEP Super Member mmb617's Avatar
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    Here you go. You probably don't want to wade through this entire thread I started 9 years ago about the exact same problem, but some of the expertise exhibited by members here can be enlightening.

    http://vb.foureyedpride.com/showthre...highlight=idle

    Cliff notes are I couldn't get the car to idle below 1400. The problem turned out to be an intake manifold vacuum leak, which was pointed out by JA Cook, a member who really knows his stuff. After replacing the gasket the car would idle at 800.
    408/T5/3.73's

    We're not fast racers, we're more what's known as half fast racers.

  6. #6

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    I'm not all that familiar with this carb which has numbers saying it's off an '85 if that changes anything. The fast idle cam which I think is located behind the choke appears to be ok I moved it around a bit but not sure where it's supposed to be at cold start. Wiggled any other linkage i could see, all looks ok. Started it, engine got to 2200 before i shut the key off.
    I'm going to see if there are any obvious vacume leaks then start doing a little searching on the 4180 to get familar with how it operates so I am more familiar with what you guys are talking about.
    Whatever happened, happened pretty quick so stuck linkage, leaking gasket, broken vacume line, clogged passage or a valve that suddenly opened or closed to de-tune the carburetor is where I'll be looking. I'm not sure if anything inside the carb could be doing this.
    Thanks for your help any ideas are appreciated.

  7. #7

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    Didn't see your post as i was writing mine, thanks for the link, I'll check it out!

  8. #8
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    Might be a simple fix like a HUGE vacuum leak. Check the hoses that plug in on the baseplate of the carb. Heat gets to those and they (along with all the wires under the hood) become brittle.

    Edit- Whoops, saw now you had mentioned looking for a vac leak above... When I bought mine it basically had the same problem you're describing and as soon as I got it home I found the gaping cracks so I got excited to toss the suggestion out there when I (almost) read the thread... lol
    Last edited by qikgts; 07-18-2018 at 08:18 PM.
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  9. #9
    FEP Senior Member 854vragtop's Avatar
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    I always add additional carb return springs to all 3 of my carbed cars. I've noticed in the past that the factory return spring was not strong enough to close the throttle plates with the engine running. Do your throttle plates snap closed with the engine running or do they seem to stay open?

    Is your choke completely open?
    Is your distributor hold down bolt tight? Did your distributor rotate and advance the timing?
    With your air cleaner on, spray some starting fluid around the base of the carb and around the intake manifold and see if anything changes with the way it runs.
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  10. #10
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    ^^^ 854vragtop is making spot on suggestions too!!!
    '85 GT

  11. #11

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    mmb617 read the thread but hoping to find something else before i pull the intake off. It's ugly in there, cracked taped up wires, zip tied connectors, pieced together vacume lines. So you think this might lead to an engine rebuild or just a total resoration? I'm sure you know the old "while you're in there" story.

  12. #12

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    I can't do any of the running tests as I'm afraid it will blow up. I shut it down when it gets over 2000 RPMs, which is immediatly. But I'll check those things i can as soon as i can get to them

  13. #13

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    Choke is closed as engine is cold. Throttle seems to close good. Distributor seemed solid, I didn't want to pull too hard on it, but seemed solid. I'll check on the cracked hoses and lines very carefully yes they are brittle.
    Of course it was running the best ever, well last 200 miles anyway, now this
    Thanks all I'll keep you posted.
    Last edited by JD302; 07-18-2018 at 08:55 PM.

  14. #14

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    OK got the idle down to about 1000. A couple things were happening. 1) The curb idle screw was indeed touching the not activated A/C kick up, backed that way away 1/4" clear. 2) I don't know if this was because the engine was cold but kept having to release that fast idle catch behind electric choke if i touched the gas pedal. 3) Even when I released the fast idle catch behind the electric choke the throttle needed to be pushed to completely closed otherwise it would stay at about 1200 to 1400 to 1800 RPMs or wherever I had pressed the pedal to.
    Which begs the question why did I have to adjust that idle screw, which I did in the chilly spring weather to keep from dying, and why was it operating fine for the last 2 weeks in 95* weather like that until now? It ran great engine wise.
    But now that I can idle it, I can check for leaks along with the other ideas.
    Looks like we're making progress, thanks to all

  15. #15

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    The curb idle screw needs to be set to be rested against something for it's idle speed adjustment, otherwise the primary throttle plates will be completely closed in their bores... backing that screw completely off won't help/solve anything. Something else is going on here... can you get us a picture like the following, showing how stiff your choke cap setting is set to?...



    ... the red plastic fast idle cam part seen in the above picture (yours might be beige, etc) is to be fully down when the engine is warmed up, otherwise it'll be engaging "fast idle". The bottom of it has steps that bump up the idle speed (fast idle) when the engine is cold, and the choke rotates everything counter-clockwise, shutting the choke plate and rotating the plastic piece with steps against the fast idle lever and adjustable screw, seen in this picture, looking from the underside...




    ... make sure that lever is not rubbing, hanging up, sticking on the back side of the choke housing, by bending it slightly away if it is...

    I don't believe you're dealing with a vacuum leak, because every vacuum leak I have met where there's a carburetor with a NOT too-rich idle transition circuit, the car will act like it's running out of gas and/or stall, because a carburetor with a correctly calibrated idle/transition circuit will not support such increased RPM's, like fuel injection WILL compensate and support such RPM with a vacuum leak. I happen to know that the 4180's have a very lean primary idle/transition circuit as is from the factory, so that's why I'm doubting a vacuum leak as the sole cause of such elevated and continuing RPM, and so with such a problem seeming to crop up out of nowhere, I would guess that either that solenoid has extended to where it extends to and has stuck there, the choke cap setting is set far too rich and keeps reengaging fast-idle, setting the fast idle into action any time you move the gas pedal, or the secondary throttle plates are not always fully closing to their proper idle position. That last bit, the secondary not fully always closing, I'm betting heavily on...
    Last edited by Walking-Tall; 07-18-2018 at 09:58 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
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  16. #16

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    Also not sure if this could be a contributing factor, on the drivers side where someone might try to jack the car up there are 2 lines coming from the gas tank to the fuel pump. Looks like someone did try to jack the car up and crushed the larger 5/16 line flat for about an inch. It was like that since i bought the car and didn't think it was causing a problem as it was running fine but i can't believe gas can get through there. There is also a lump in the floor near where your left foot rests where it looks like they moved the jack after they crushed the line.
    Should that be repaired first or is that a return line. I would hate to adjust the carb. then have to readjust after i replaced the line, if this is all related,
    thanks

  17. #17

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    I'll try to get a picture and post. My choke is set 3 notches lean. My black fast idle cam can be pushed down however as engine is only slightly warmed i had to push it down and each time I move the throttle it resets so I hear 2 clicks pushing it back down. I did notice a very slight opening on the secondary throttle plates not sure how much is too much but I'll get a photo of that posted too, thanks

  18. #18

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    There you go then. All times you have to manually rotate the fast idle cam clockwise, and get the two clicks pushing it back down. There's only one thing that rotates everything counterclockwise, and that's the thermostatic spring inside the choke cap when it's cold... or not registered correctly inside the choke housing with the little metal tab that connects with all else outside when it was put back together... the choke cap is set far too rich, you have no voltage connected to it to operate like an electric choke should, or the bimetal thermostatic spring's loop inside was not correctly engaged with the metal tab inside there...
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  19. #19

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  21. #21

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    Do you think the choke somehow changed or got loose? (It was working fine in 40* weather and just recently in 95* weather.) Or was that just part of the issue and having to kick it down right away was an indication things were not well? The car wouldn't start unless I pressed the pedal and reset it and it always started high idle so i would have to pop the pedal to knock it down then was fine.

  22. #22
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    "Jiggle" may have been the wrong verb. With the engine off, grab the secondary throttle shaft and turn it to open the secondaries, then let it close on spring pressure, then firmly turn the direction to close the secondaries. If you feel any movement that direction, something is sticking. Repeat this a few times to get the feel.

    If the engine wasn't fully warmed up, I wouldn't worry about the high idle cam yet. You might have more than one carb part gummed up after the car sat for a long time.

  23. #23
    FEP Super Member erratic50's Avatar
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    I had a throttle cable go bad once. It would stick before it returned all the way. make sure when you are at idle that the throttle is resting on the idle screw on the carb.

  24. #24

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    Yes I think there are several items compounding effects and throttle cable is part of that. I just removed the cruse control which is non-operational anyway to get better access to the throttle cable, thanks

  25. #25

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    May have problem solved. I've driven the car only 15-20 miles so far but all seems well. I think the secondaries were sticking ever so slightly open yes very difficult to tell if it's closing each time and perhaps the A/C solenoid idle set screw location may have moved. As suggested an extra throttle spring will hold things tight. I sprayed clean the inside of the carb, bores, plates etc. Outside I sprayed the linkage. Then adjusted the idle set screw to rest on the A/C solenoid. Seems to have done the trick.
    Thanks for the wealth of experience and willingness to share

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