By on December 21, 2018

2016-Hyundai-Tucson-Engine, Image: Autoguide.com

Steven writes:

Hi Sajeev,

I have a 2016 Hyundai Tucson 1.6T with 90K and I have an intermittent issue of a rough idle with the A/C on — it feels very jumpy and did not have this issue before. When you turn it back off the idle becomes smooth again. I’ve cleaned the MAP and boost pressure sensors as well as removed the throttle body to clean it — it had a little gunk at the bottom of it but it looked really clean. That seemed to clear up the problem, but the issue came back again. I know it’s due for another spark plug change (as Hyundai says every 45K) so I’ll get that done soon. but I’d like to trace this down while I’m doing the work under there.

Any ideas?

PS: And no, it’s not under warranty — as countless others have claimed.

Sajeev answers:

Any engine codes? It never hurts to scan for codes just to cross it off the list.

That said, I am leaning toward either a vacuum leak (not likely, but modern turbocharged and direct injected mills got plenty of plumbing) or a refrigerant pressure problem.  If you used a cheapo A/C recharge kit (again, not likely) get a pro (or professional gauges) to test the actual pressures: maybe your expansion valve (some cars use an orifice tube) is blocked and causing pressure issues that’s driving the engine computer bonkers.

But this is a direct injected motor! Fouled spark plugs and coked up EGR passages/combustion chambers (though high mileage suggests otherwise) could exacerbate the poor idle when the A/C compressor starts churning. So replace the plugs, but put a scope in there before installation: do you see significant carbon buildup?

Hopefully not, but if the plugs give you no joy, maybe it’s time to de-carbon the engine as per Hyundai specifications.

What say you, Best and Brightest?

[Image: Autoguide]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.


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48 Comments on “Piston Slap: Roughing It in Tucson?...”


  • avatar
    MrGrieves

    By 90K miles (with a DI engine) your intake valves should have a healthy coating of carbon. I’m not sure if Hyundai has this issue at the same magnitude as VW, BMW, etc… but I’d recommend the ol’ Walnut Shell Blast if a scope warrants it. Oh, and don’t waste your time with intake or fuel treatments, they won’t work.

    • 0 avatar
      gtem

      Agreed, I’d be scoping the backs of the valves to see if there’s a lot of buildup. Welcome to the wonderful world of direct injection!

      • 0 avatar
        ToddAtlasF1

        Don’t worry. The DI era will pass once nothing else is available. Governments will suddenly decide that their particulate emissions demand the same sorts of drastic actions that they decided diesel particulate emissions merited after many countries forced them down their subjects’ throats.

        • 0 avatar
          scrappy17

          We are already there in Europe. Google Gasoline particulate filters.

          Euro 6C regulation requires it, and almost all DI engines sold in Europe already have it in place.

    • 0 avatar
      Art Vandelay

      Yeah, trade it in for a malaisemobile with a quadrajet and a 110 hp V8. Cos everyone knows them fancy turbos and injection is gonna blowed up early.

      I’d look when you do the plugs, for sure…but typically these issues are one of the myriad of things that have made cars idle rough for decades, not carbon buildup.

      • 0 avatar
        CaddyDaddy

        Yeah, trade it in for a malaisemobile (mid 90’s) with a quadrajet (TBI) and a 110 (205HP SBC) V8. – There, fixed it for you. That was peak Car!

        • 0 avatar
          Art Vandelay

          Design wise, the 90s we’re peak car. But every reliability statistic says cars are better nowadays. And when I look back at the performance numbers for a 93ish Mustang GT vs. my Fiesta ST I am reminded we really do live in a golden era. Except for looks, cars are just better nowadays. I want my car in a B13 SE-R body. But if I have to pick between the 2, I’ll take today’s stuff

      • 0 avatar
        ajla

        What if there was something in between a 1980 Olds 260 and a GDI-T engine? Imagine if it could even help keep valves clean *and* have lower emissions?

        • 0 avatar
          Arthur Dailey

          I am concerned that in the future we might view DI and possibly also CVT’s in the same way that we look at the ’emission control’ devices of the early/mid 1970’s.

          Stop gap measures, used until better technology became readily available.

          • 0 avatar
            ToddAtlasF1

            That would be nice, since it suggests that superior technology will one day be legal again.

          • 0 avatar
            Featherston

            Totally agree, Arthur. In response to scrappy’s and Todd’s comments above, a positive outcome of stricter particulate regs in Europe is that VW/Audi has started adopting dual injection. (The analogous US-market engines still are DI-only.)

            I’ve commented to gtem in other threads that DI seems to be the unhappy medium between port injection and dual injection. All three models have pluses and minuses, but to me DI-only is clearly the worst of the three. It’s kind of vexing that it’s the industry default at this point.

            As for CVTs, I’m morbidly curious to see how this latest generation of compacts and subcompacts shakes out. Not to be too pointed, but do all CVTs have sketchy durability or do Jatco CVTs have sketchy reliability? As someone who’s gotten great service out of 3, 4, and 6-speed slushboxes, the trend toward CVTs is disappointing. (Pet peeve: When people cite the Prius’ transmission as evidence that Corolla CVTs will be durable. Not. The. Same. Thing. At. All.)

          • 0 avatar
            PrincipalDan

            I keep crossing my fingers that more manufacturers will adopt dual injection. It doesn’t seem to be hurting Toyota’s fuel economy.

            And Toyota’s may be boring but the company is so dang conservative I see their rejection straight DI as an effort to not pay a bunch of carbon build up warranty claims.

            I’d be tempted to install a catch can on a straight DI engine in my fleet but then I’m sure that it can’t be done until the warranty is up.

          • 0 avatar
            Featherston

            At PrincipalDan – Toyota is an interesting case study because of their V6’s:
            – Port-injected transversely mounted 3.5’s, apparently no issues.
            – Dual-injected longitudinally mounted 3.5’s, apparently no issues.
            – DI-only longitudinally mounted 2.5’s, German-esque carbon issues. My understanding from internet chatter is that a lot of 2.5 cylinder heads have been swapped out or removed and cleaned under warranty (although perhaps a BMW-style walnut shell cleaning would’ve provided x thousands of miles of better running).

            It’s early in the game yet, but the 8AR-FTS in an NX 200t I borrow on occasion is running smoother at four years and 50,000 miles than it was two years ago. That’s with nothing but scheduled fluid and filter changes. And it’s a vehicle that makes a lot of short trips which theoretically could could induce carbon build-up.

            I take Ford’s recent-ish adoption of dual injection as a good sign. Hopefully the whole industry will be there soon.

        • 0 avatar
          afedaken

          Like… say… A Toyota?

      • 0 avatar
        gtem

        Funny you bring up the malaise era, because I’d point a few of the current problem-prone areas (DI, CVTs, aggressive torque converters causing transmission problems, diesel emission equipment issues, fragile timing chains) as revisiting that era of manufacturers wrestling with new requirements on emissions and fuel economy.

        We’ll get past it, but insinuating I’m a Luddite just because I’m leery of a technology with KNOWN issues over the last several decades.

        FWIW, the DI Tacoma 3.5L I just rented to drive to Chicago and back did not get appreciably better MPG than my ancient iron-block 3.4L port injected 4Runner (19mpg for both), and with the way the throttle was mapped and transmission was tuned, actually felt weaker on mild hills: mine very rarely needs to drop out of locked up converter in 4th gear anywhere in the Midwest.

        • 0 avatar
          Featherston

          Well said, gtem. The frustrating aspect of these changes is that, generally speaking, this is the first time since the 1970s that we’ve seen the industry backslide in terms of reliability and durability. That frustration doesn’t make one a Luddite.

          Q: Are people really experiencing issues with the latest conventional automatics? I know that the scribes moan and complain that they’re “busy”, but are there widespread reliability or durability issues with the latest crop of 8, 9, and 10-speeed automatics?

          • 0 avatar
            gtem

            The issue I’m referring to specifically are Toyota’s 6spd automatics on cars like the Camry, which since 2012-ish have been tuned to lock up very aggressively in lower gears at really low RPMS, and to stay locked under some load. I know my wife’s was reflashed at one point per a TSB (without us asking for it) and then Toyota followed up with an extended warranty out to 150k. Per my Russian sources, that increased torque-shock is a real issue with reduced longevity resulting. I like keeping the automatic “locked on” in terms of feel most of the time, but when it comes at a cost of durability, or inducing unpleasant vibrations as the transmission lugs a 4cyl engine along at 1000 rpm, that’s a bridge too far. The classic 4spd transverses Aisin in my ’96 ES300 absolutely wiped the floor with the newer 6spds in terms of smoothness, and had no signs of excessive wear or imminent failure when I sold it at 209k miles.

            I still haven’t fully wrapped my head around Toyota’s new 8spd, is it a DCT with a torque converter or not? I know that it is physically very compact and light, an impressive engineering feat no doubt but I’ll wait and see how it holds up. I’ve driven a few ’18 Camry rentals (4cyl+8A) and they feel remarkably strong but refinement has taken a notable hit. Fast acceleration yields some very satisfying crisp shifts, but around town it’s busy, especially in situations like a mild hill at 35mph and you give it a bit of gas.

          • 0 avatar
            Art Vandelay

            I just get sick of all the hate on here. If it isn’t a Ford Panther or a stripped Toyota Tercel you paid cash for at 30 percent off invoice in 1992 and put 400k on it sucks. The world has moved on.

        • 0 avatar
          Art Vandelay

          Cars are the most reliable and long lasting than they have been in the history of the automobile by every measurable metric. It isn’t being a Luddite, I think it’s just nostalgia. Everyone looks back on the good cars from the era. Nobody thinks about all those Dodge Shadows, Toyota Paseos, Nissan Stanzas, Chevy Luminas, Ford Escorts and other crapboxes that disappeared from the road a decade ago. They are ugly…this I give you but most of that is regulatory. If you aren’t enjoying the stuff you can buy today you are missing out and I am a hopeless nostalgic as well that bids on at least one gen-x mobile on bring a trailer weekly (currently an 85 Celica and a 99 BMW. But it is because of nostalgia, not because I am under any illusion that they are better than anything currently in my driveway/garage (15 f150 being the oldest).

          • 0 avatar
            gtem

            To be honest a 1990s Stanza was a much better car relative to its contemporaries than a current Altima is, and with a good driver I bet a 5spd Stanza with the KA24 could walk a current CVT one. I’d be willing to bet than a 1990s Escort would last longer than a Powershifted modern one.

            I like the 90s-2000s because we seemed to hit a sweet spot in things like paint quality, driveability, had good quality multi-port fuel injection and ignition systems, and cars from that era (IMO) strike a satisfying balance of comfort and driver engagement (for those who care about that sort of thing). Now we have sound tubes plumbed in and buttons to vary the heaviness of our lifeless electric steering, while we sit on nasty scratchy cloth seats.

            I may be nostalgic, and won’t deny the strides in safety and power/fuel economy and average reliability, but we lost some very good attributes as well, and I shudder to think how your Ecoboosted F150 will hold up in 20 years as far as maintenace/repairs go. I do like the use of aluminum as a way to fight rust.

          • 0 avatar
            Art Vandelay

            As one who owned multiple 90sescorts, I’ll take that bet all day and twice on Sunday.

        • 0 avatar
          Art Vandelay

          I don’t get the low mileage in the Tacoma. That is well below what my crew cab F150 pulls on highway jaunts. Winter gas maybe or some seriously lackluster engineering.

  • avatar
    Arthur Dailey

    My 1st Hyundai, with 110,00 miles has a different, but somewhat similar (an oxymoron) issue. At low speeds, usually around the 1st gear to 2nd gear shift change but sometimes also at the 2nd to 3rd shift (yes it is a MT), the engine sounds like an old domestic v8 with the air filter lid ‘flipped’. At one point I even thought that a motor mount had come loose/broken or that part of the exhaust had come loose.

    Changed up what I can, gave it an ‘Italian tune-up’. For some reason it dissipated, somewhat, when I ran the gas tank nearly dry then used only ‘premium’ for a few fill ups.

    • 0 avatar
      R Henry

      Methinks sticky IAC.

      • 0 avatar
        Arthur Dailey

        Thanks but in my case, it does not appear when idling. Only when shifting, in the lower gears. Generally on the up shift.

        • 0 avatar
          gtem

          FWIW Hyundai’s recommendation for all their current DI motors is to only use ‘Top Tier’ fuel, and if not, then periodic use of fuel injector cleaners. I fail to see how that recommendation could help the backs of valves gunking up, but perhaps they’re worried about the actual injector nozzles as well.

          • 0 avatar
            MBella

            Actual injectors. The nozzles are so fine that they gun up quickly. The varnish either restricts flow, or keeps the valve from completely sealing and you get a fuel leak into the cylinder causing other issues.

  • avatar
    crazyforwheels

    I’m not familiar with Hyundai engine mechanics, but, maybe I can give you a new thought path.

    Years ago I worked for a OEM manufacturer, and we made a under the hood switch that stepped up the engine idle speed when the a/c was turned on.

    Since your non-a/c idle is smooth, I am thinking you should ask the hyundai dealer if such a switch exists. If so have it checked out for operation.

    • 0 avatar
      Scoutdude

      That would have been many years ago. In today’s cars the climate control panel does not control the A/C compressor. It sends a signal to the PCM who decides if the A/C compressor can be engaged and if it decides to engage it adjusts its control strategy accordingly.

      • 0 avatar
        MBella

        It depends on the car. Many compressors and clutches are controlled by the climate control module. That being said, it communicates over the CAN and the engine will know to compensate for it

  • avatar
    NeilM

    Here in the 21st century idle speed is regulated by the ECU acting on either the drive-by-wire throttle plate, or via an electrically operated idle control valve that bleeds a little extra air into the intake tract downstream of the throttle plate.

    I’d guess that either something in the idle control system isn’t working right, or the A/C compressor is defective (not enough oil? excess charge?) such that it’s imposing a load that’s greater the idle control system can handle.

  • avatar
    PrincipalDan

    PLUGS EVERY 45K?

    What the hell happened to 100K to 120K plug changes?

  • avatar
    Halftruth

    Since it has not been mentioned yet, try this.. Disconnect the clutch wire to the AC. Retest. If it smooths out, the issue is in the AC or the belt etc. If it does not smooth out then something in the idle control circuit possibly. I had a sticky (and dying clutch) do this to me and while the idle was not as bad as described here, it came close. Replaced clutch assy and done. That is not to say you may have a wonky belt or pulley at that mileage though..

    Good luck

  • avatar
    Raevox

    It’s for this reason, that I will be installing dual catch-cans in our Elantra GT Sport, this Spring.

  • avatar
    Hummer

    Direct injection and turbos are like diesel emission equipment, you know your getting into a headache when you buy it, but unlike diesels, DI is never really worth the hassle of dealing with.


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