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    #1

    erratic engine speed

    Recently my car (351 police-style motor with 7200VV carb) has been behaving very strangely. It suddenly decided to idle more slowly, or at least more roughly, and is changing engine speed in a non-rhythmic way, at idle and with throttle input. Even if I put my foot on the gas in park or drive, it won't hold a steady engine speed or acceleration. Let's say I set the speed in neutral/park at 2000RPM with the gas pedal, it'll climb or dip or one than the other without me changing the throttle input. The same thing can be felt while driving.

    It feels like it's also bogging off-idle, but I'm not sure that's connected or even happening, considering the throttle input just isn't reliable. If I hold the wheel full-lock, loading the power steering pump (yeah I know it's a bad idea) the engine will almost die in drive, and the RPM's go noticeably lower even in park. This wasn't the case previously.


    I know it's running a bit lean by checking plugs, but that shouldn't affect anything since it's been like that since I got it. Other than that though, I don't have any real ideas.

    85 4 door 351 Civi Crown Victoria - Summer daily driver, sleeper in the making, and wildly inappropriate autocross machine
    160KMs 600cfm holley, shorty headers, 2.5" catted exhaust, 255/295 tires, cop shocks, cop swaybars, underdrive pulley, 2.73L gears.
    waiting for install: 3.27's, Poly bushings, boxed rear arms, 2500 stall converter, ported e7's, etc

    06 Mazda 3 hatch 2.3L 5AT (winter beater that cost more than my summer car)
    Tags: None
    #2
    Have you checked for vacuum leaks? Those will play havoc in any carb system, and if your car is still factory setup as far as vacuum lines go you have a shitload of things that can cause leaks...

    Comment

      #3
      does sound like vacuum leaks to me as well. Tons of lines on those cars.
      86 Lincoln Town Car (Galactica).
      5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

      91 Lincoln Mark VII LSC grandpa spec white and cranberry

      1984 Lincoln Continental TurboDiesel - rolls coal

      Originally posted by phayzer5
      I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

      Everything looks like voodoo if you don't understand how it works

      Comment

        #4
        That does make sense. I've always suspected there were undiagnosed vacuum leaks somewhere. It is bone stock, included a/c, smog pump, etc, so yeah it's an insane rat's nest of hoses. Most of the rubber stuff looks good, though, and I've patched the issues I could find in the harder thinner plastic stuff. I guess more time with a flashlight underhood.


        Weirdly, after about 15-20 minutes of driving, the idle speed became ridiculously fast, instead of slightly slow. I don't have a tach, but easily 2200RPM going by ear, in neutral. I hit 35KMH (23?mph) without touching the gas. It was still unstable in terms of RPM's, but not as badly as before. I adjusted the idle speed so that it was still annoyingly fast, but at least didn't sound like I was sitting there with my foot on the throttle. It's pretty perplexing that the engine idles faster once it's warm, instead of a fast-idle to heat it up.

        I should really just park it for the winter and rebuild the carb while it sits, but after the epic frozen-locks saga, I'd like to celebrate by having a (mostly) functional car for at least a week.

        85 4 door 351 Civi Crown Victoria - Summer daily driver, sleeper in the making, and wildly inappropriate autocross machine
        160KMs 600cfm holley, shorty headers, 2.5" catted exhaust, 255/295 tires, cop shocks, cop swaybars, underdrive pulley, 2.73L gears.
        waiting for install: 3.27's, Poly bushings, boxed rear arms, 2500 stall converter, ported e7's, etc

        06 Mazda 3 hatch 2.3L 5AT (winter beater that cost more than my summer car)

        Comment

          #5
          you got a big vacuum leak somewhere man, and I mean big! Start pulling the 3/8" lines, PCV and brake booster come to mind here.

          Comment

            #6
            I hear a hissing that sounds like it's right in front of the carb, maybe the PCV (is that what's going from the front of the driver's side VC to manifold vacuum port right in front of the carb?) but It's hard to tell if it's a vacuum leak or just the shrill sucking from the carb itself.

            Does it sound like the leak got bigger/another one started when the idle got faster, or is it doing that a symptom of it having been leaking since the start of my problems?


            Also, if I pull the PCV lines, would I have to plug both ends or just at the manifold?

            85 4 door 351 Civi Crown Victoria - Summer daily driver, sleeper in the making, and wildly inappropriate autocross machine
            160KMs 600cfm holley, shorty headers, 2.5" catted exhaust, 255/295 tires, cop shocks, cop swaybars, underdrive pulley, 2.73L gears.
            waiting for install: 3.27's, Poly bushings, boxed rear arms, 2500 stall converter, ported e7's, etc

            06 Mazda 3 hatch 2.3L 5AT (winter beater that cost more than my summer car)

            Comment

              #7
              Since it seems to be time or temperature related, I'd be looking at stuff that runs through the temperature vacuum valve things.

              Don't eliminate the PCV. It does good things for your motor, including oil control and sucking blowby out of the crankcase so the oil doesn't get contaminated. And yes, the line goes from the valve at the driver's side valve cover to the front of the carb. I would be looking at the line to ensure its sealed at both ends tho. They have a habit of becoming hard as a rock and not sealing properly.

              You might also try spraying some wd40 or something around the base of the carb. If you have a leak at the gasket, you should hear the idle change. Make sure the carb mounting bolts are present and tight too. Don't laugh, I've seen things running with missing carb bolts or nuts.
              86 Lincoln Town Car (Galactica).
              5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

              91 Lincoln Mark VII LSC grandpa spec white and cranberry

              1984 Lincoln Continental TurboDiesel - rolls coal

              Originally posted by phayzer5
              I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

              Everything looks like voodoo if you don't understand how it works

              Comment

                #8
                I guess I should have explained a bit better, bu pulling lines I meant not removing them and capping stuff off, but pulling them off one at a time to inspect them - often the rubber looks good on the outside, but is actually rock-hard at the ends and don't seal like it should. Honestly in your position I'd go on a vacuum line replacing spree, ditching all the non-essential emissions BS in the process.

                Comment

                  #9
                  I mean removing temporarily to diagnose, not drive around without them. I guess what I meant was, would having the PCV open at the valve cover matter in terms of vacuum leaks and related issues if the manifold side was sealed.

                  A lot of the lines do bulge out and seem stiff at the ends, in fact I think that may be my problem at the PCV valve. I'll take the advice and start replacing the lines that seemed questionable at the ends.

                  85 4 door 351 Civi Crown Victoria - Summer daily driver, sleeper in the making, and wildly inappropriate autocross machine
                  160KMs 600cfm holley, shorty headers, 2.5" catted exhaust, 255/295 tires, cop shocks, cop swaybars, underdrive pulley, 2.73L gears.
                  waiting for install: 3.27's, Poly bushings, boxed rear arms, 2500 stall converter, ported e7's, etc

                  06 Mazda 3 hatch 2.3L 5AT (winter beater that cost more than my summer car)

                  Comment

                    #10
                    Thanks a lot guys. I took a closer look at the PCV valve, and it was badly cracked, leaking quite a bit. I bought a new PCV valve and some 3/8's inner diameter rubber hose, as well as some other smaller size. The hose from the hard line to the PCV valve got replaced. Big difference. Better power off-idle and a much smoother (and slower) idle. It still isn't perfect, but it's about what it was before.

                    I'll start replacing other hoses as time allows. What size is the hose that is used.. pretty much everywhere? Smog pump, to the carb, on top of the air intake, etc.

                    85 4 door 351 Civi Crown Victoria - Summer daily driver, sleeper in the making, and wildly inappropriate autocross machine
                    160KMs 600cfm holley, shorty headers, 2.5" catted exhaust, 255/295 tires, cop shocks, cop swaybars, underdrive pulley, 2.73L gears.
                    waiting for install: 3.27's, Poly bushings, boxed rear arms, 2500 stall converter, ported e7's, etc

                    06 Mazda 3 hatch 2.3L 5AT (winter beater that cost more than my summer car)

                    Comment

                      #11
                      Haha, so I haven't lost my touch with carbs yet, goodie that you got her fixed up at least patially! About the rest of the lines, it's usually some small shit, like 5/32" or so, up to 1/4" for the larger vacuum hoses.

                      Comment

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