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02 Daihatsu Cuore/Mira L700 1.0 running rough in low RPMs- head gasket, vacuum leak?

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  • 02 Daihatsu Cuore/Mira L700 1.0 running rough in low RPMs- head gasket, vacuum leak?

    Hey guys, here's what I'm dealing with:

    02 Daihatsu Cuore/Mira L700 1.0

    symptoms:
    - Idle is kinda rough. It's a 3 cylinder, so I don't expect super smooth idle, and I never had one of these cars, but I fell like it can't be normal.
    - there is a noticeable hissing sound around the throttle body: https://www.youtube.com/watch?v=4HJFijZUuz0 But I couldn't find any leak (yet), is it possible that sound is normal? I tried removing the airbox, starting the engine, opening the throttle a little bit, and I blocked off the IACV passage. The hissing gone away. So I think the hissing might be normal?
    - It holds 1000rm idle, doesn't bog down, but is not responsive in low rpms (1000-3000).
    - The idle doesn't sound irregular, but I feel like it has to be smoother.
    - it's got a noticeable vibration on idle - the airbox visibly oscilates maybe 5mm and the bonnet shakes when stopped on lights too.
    - Doesn't have too terrible bottom end, but I feel the engine is not happy under 3000.
    - Over 2500/3000 it runs great and sounds healthy
    - I don't think it smokes

    additional info:
    - low mileage car, under 50k (wasn't driven much, was sitting often, but not for years at a time afaik)
    - everything stock
    - oil when I bought it was pretty old, black, but not low.
    - there was some moisture and hints of rust on upper parts of the dipstick, but the oil itself was not milkshaky
    - coolant was a bit low, but clean. Red type.
    - oil pressure light was kinda slow to go off after starting, took maybe 3 seconds to turn off. Stayed off and never came on when driving. After I replaced the oil it turned off instanly after starting.
    - I added injector cleaner additive into the fuel tank, had no effect on running
    - I changed the oil. After driving for some time, there were some hints of milkshakey substance in the oil cap, but only tiny bit. I'm hoping it's just condensation from sitting too long? The oil itself looks still clean and I can't see any milkshake on the dipstick on looking down the engine through oil cap
    - I cleaned the throttle body and IACV. It was dirty, but not the worst I've seen. Cleaning had no effect.
    - I checked the sparkplugs, there was some deposit on them, the worst one looked like this: 20201103_140854_01.jpg
    - I didn't replace the sparkplugs yet, just wirebrushed, but had no effect
    - I topped off the coolant. It doesn't seem to be using any, and the colant itself still looks clean
    - when I remove the radiator cap and start the car, there's no bubbles coming out


    Questions:
    - is that hissing sound normal? It's likely IACV related.
    - is there anyhting else I can check? Does it have an EGR? I couldn't finy anything like it
    - I should probably buy new sparkplugs anyway, but I feel like they ar emerely a symptom
    - could my head gasket be blown? I feel like it's too early for that (the car has only 50k, and wasn't driven hard)

    Thanks for any help or ideas!
    Last edited by Redmouse; 04-11-2020, 09:08 AM.

  • #2
    It does indeed SOUND like one hell of a vacuum leak.

    At 37 seconds (almost 38) of your video, bottom left, on the black boxy thing; is that an open tube?
    I just notice all the other 'caps' don't have hose clamps, but that one does....

    Get a mate who smokes, or buy the worlds cheapest vape pen, and start looking for the air leak.

    Comment


    • #3
      Hello again!
      Good eye on the cap thing, but it's a proper cap sadly, that wasn't the leak.

      I got one possible lead, looks like the gasket of the IACV might possibly not be good. I didn't have a replacement on hand, so I just used silicone - have to wait until it cures properly to test.

      Comment


      • #4
        Randomly I found this german video with the same exact hissing sound. Might be normal then, or very common fault https://www.youtube.com/watch?v=cIyjyVzotlY

        Comment


        • #5
          It's a bizarre noise though that's for sure....
          I know those engines have a terrible case of oil consumption when revved high often, due to oversized breathers.
          I wonder if it's perhaps a stuck open PCV or some such?

          When it comes to maintenance, the PCV Valve is probably the most overlooked part of any modern engine.
          75% of them I see are clogged open, and they only need brake cleaner to free them up until they rattle freely.

          - I added injector cleaner additive into the fuel tank, had no effect on running
          Just a tip; never bother with that, read the ingredients, on MOST of them, it's just "9XXml/L Hydrocarbons", and the bottle is usually only 250-500ml... in otherwords? It's usually just a shot of Ethanol.
          There are exceptions out there, like Fuel Doctor, but most are just various unclean hydrocarbons that can't sell anywhere else, because they're not refined enough.
          So do the math, 40L Tank, 400ml of Ethanol? You have just made E1 fuel; 1% Ethanol.

          If you want to run 'injector cleaner' your best bet, even on cars that "don't recommend E10 Fuel" is to just use HALF a tank, of E10 (making it E5).
          E10 fuel needs on average 3% more fuel per combustion, this is often the upper limit of a short term fuel learn in the ECU.

          By running E5 (1.5% more fuel for stoich), one of two things will happen.

          It will run 1.5% leaner (99% of everyday cars have MUCH more tolerance programmed in than that; it wouldn't scare me at all) or it will use 1.5% more fuel (because it's within the limits allowed to be 'learnt' short term).
          Either way, you're getting 5X the cleaning effect of a cheap bottle of injector cleaner.

          Never run E-Anything, if you have CORK gaskets, like classic 70's VW engines, for example.
          Nothing 80's onwards has them, to my knowledge.

          Anyway, if you rule out there's no air leak, and things like PCV are happy, etc etc, a rough idle, but fine cruise, is often a fuel filter thing.
          Have you checked the filter?

          It sounds counter-intuitive, because most 'normal' cars have a single speed pump, so wouldn't it get MORE fuel pressure at idle?
          Yes, and no.
          First, a car can run 'smoothly' much leaner at speed than at idle (I didn't say safely, i said smoothly).
          Second, Often cars will generate about 12.X-13 volt at idle, where as they'll jump to about 14v at rev; it doesn't seem like much, but increasing a DC voltage pump by 5% can be one hell of a flow difference, especially if there's a blockage (old filter) creating back pressure.

          These are all things that are 'good to do', reality is we're being pedantic, the car could run like that for another 10 years, but hey, we're MCM-crew, fixing little things in out nuggety cars is what we do.

          Comment


          • #6
            Yea that is one massive vacuum leak for sure.

            Maybe you should look more into that IACV. I'm quite sure it's faulty.
            1982 Ford Taunus

            1984 Ratty Oldsmobile Custom Cruiser

            1963 Oldsmobile Super 88

            1974 Chevrolet El Camino

            Comment


            • #7
              Originally posted by SBC View Post
              Yea that is one massive vacuum leak for sure.

              Maybe you should look more into that IACV. I'm quite sure it's faulty.
              I'm not so sold on the IACV personally; but he can check easily.
              You could still be right.

              If it's a faulty IACV there should be a MASSIVE change in engine idle quality with air-con on vs off.
              If it doesn't have working aircon, then Thermo Fans will also cause the same (just more mellow) effect; just let it idle up to temperature.

              Comment


              • #8
                Thanks guys!

                So I did some wrenching in the meanwhile, and I determined:

                - the idle is probably normal like this. Apparently it shakes like an expensive dog from the factory, because all other videos of Daihatsus running had the engine shake just like mine. I'm just spoiled by 4 cylinders I guess.

                - the hissing sound is caused by the IACV passage, and is only loud when the idle is set high (over 900 rpm) by rotating the plastic IACV actuator. I set it to 900, which felt like a reasonable middleground between hissing and engine shaking too much.

                - the IACV gasket at the bottom of the throttle body was swolen, and probably played some part in the possible coolant consumption. Because it also seals coolant passages in the throttle body. It could possibly be leaking a tiny bit, just enough to show coolant deposits on the sparkplugs over longterm.

                - I also checked the injectors, all had nice identical spray pattern and the fuel rail was pristine inside

                - put in new sparkplugs, had no effect

                - looked for a PCV valve, but as far as I can tell, it doesn't have any. There is just a straight trough hose without any valve, it was free both ways.

                So I guess I'll leave it be and declare it a factory nugget.

                Comment


                • #9
                  Master_Scythe, so could I possibly just add 2L of E85 into a tank and run it like that?
                  I'll try to have a look at the fuel pump and filter, but I doubt it's faulty. When priming it sounds perfectly fine, and everything else on the car is nice and clean.

                  Comment


                  • #10
                    Originally posted by Redmouse View Post
                    Master_Scythe, so could I possibly just add 2L of E85 into a tank and run it like that?
                    I'll try to have a look at the fuel pump and filter, but I doubt it's faulty. When priming it sounds perfectly fine, and everything else on the car is nice and clean.
                    Its far too early for that math >< lol, but If it adds up to less than 10% ethanol, then yep.

                    Chemical tuning can be a thing.
                    Had a mates Subaru which had failed MAF and o2 sensors but we needed to drive home.
                    External wideband said it was running at a fixed 10:1
                    Half a tank of E85 Brought it up to 11.5:1 which was at least drivable.

                    Comment


                    • #11
                      Regardless; fuel filters (leave the pump) are like $10, if you haven't done it, just do it.
                      It's cheap, and 90% of the time no previous owner ever has.

                      As we saw in the episode where they bought taytay back, it still ran just fine, even in high performance drifting; but they literally took MUD out of the filter when they dissected it.

                      Worthwhile $10.

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                      • #12
                        Heyy, I'm back! So it was the O2 sensor! Wrong mixture, making the car run rough and have not great fuel economy.

                        For now I replaced it for a used one from a different car (Nissan March ) and it runs much better now. But I will order a new proper one, and report back.

                        Comment


                        • #13
                          Originally posted by Redmouse View Post
                          Heyy, I'm back! So it was the O2 sensor! Wrong mixture, making the car run rough and have not great fuel economy.

                          For now I replaced it for a used one from a different car (Nissan March ) and it runs much better now. But I will order a new proper one, and report back.
                          Yea that picture you had from the spark plug shows it runs lean, but I was so sure it's just a massive vacuum leak. That hissing sound was something I had never heard before on a engine that doesn't have a vacuum leak.
                          And if you have huge vacuum leak the engine runs super lean also.

                          Good thing that you found the problem.
                          1982 Ford Taunus

                          1984 Ratty Oldsmobile Custom Cruiser

                          1963 Oldsmobile Super 88

                          1974 Chevrolet El Camino

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