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  • Rough Idle After Warmup

    I have this strange issue where my tudor will idle beautifully after just a few minutes of running but once it warms up to normal operating temperatures, the idle is extremely rough to the point where you think that the car might die on you. The car however does fine driving down the road and under load but once you stop at a stoplight, the car runs terribly. I also experience a hesitation in throttle response from idle. I'm thinking it might be a cracked intake manifold that is fine when the car is cold because the crack is retracted and not letting a whole lot of air in and when the car warms up, the crack expands allowing more air in creating a lean mixture. What are your thoughts?

  • #2
    Yup, sounds like a vacuum leak. Spray some MM on the intake, that will tell you if that is leaking by running good for a few seconds.

    Comment


    • #3
      As always make sure your basics are set to specs, points etc. What happens if you cup your hand over the air horn or using the choke plate to restrict the air flow? Does it get any better? I like to use my hand this way i can meter how much air i am letting through. By doing this it richens the mixture so if there is a vacuum leak it can sometimes help smooth it out.
      Heat usually expands a crack / closes it up!
      3 ~ Tudor's
      Henry Ford said
      "It's all nuts and bolts"


      Mitch's Auto Service ctr

      Comment


      • #4
        Originally posted by Mitch View Post
        As always make sure your basics are set to specs, points etc. What happens if you cup your hand over the air horn or using the choke plate to restrict the air flow? Does it get any better? I like to use my hand this way i can meter how much air i am letting through. By doing this it richens the mixture so if there is a vacuum leak it can sometimes help smooth it out.
        Heat usually expands a crack / closes it up!
        Ignition system was entirely overhauled 2,000 miles ago. Points are checked every 500 miles to ensure proper gap. Good and consistent spark. Again, idles great when cold and just warming up but once it's all warmed up it just will not idle smoothly. Like you said, a leak should present it self when it's cold and close up when the metal expands and closes any gaps. I'm truly stumped on this one.

        Comment


        • Mitch
          Mitch commented
          Editing a comment
          It could just be a gasket and not a crack. try the restricting the air flow method or carb clean

          You can also meter the carb clean into the vacuum wiper port if you have one

      • #5
        I like to use an unlit propane torch to check for leaks.

        BTW, I know some foreign countries call a flashlight a "torch", so then what do they call a propane torch?

        Comment


        • #6
          After setting the basics you need to determine whether you have a spark, or a fuel issue. This can be done by using an inline spark tester, can of carb cleaner, and a fuel bowl float level tool when running. Spark and fuel are always blamed on each other and it usually turns out to be the other. How are the plugs burning?

          Just some of the main things:
          Running lean (vacuum leak, fuel delivery)
          Running rich (weak spark, carb issue)
          Weak or erratic spark ( condensor, ignition circuit issues, plate wire, or wireless plate)

          Doing a diagnosis will lead you up the next trail

          https://www.vintagefordforum.com/for...rmittent-spark

          https://www.vintagefordforum.com/for...-and-misc-tips
          3 ~ Tudor's
          Henry Ford said
          "It's all nuts and bolts"


          Mitch's Auto Service ctr

          Comment

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