Hooniverse Asks: What's The Most Bizarre Instance of Cause And Effect Car Malfunction You've Ever Seen?

I read an article in Skinned Knuckles a few years back about a Studebaker Avanti that was thought to be haunted. The issue was that when accelerating away from a stop the car would suddenly rev like crazy, leaping forward. This of course was a pretty dangerous activity. The owner had gone over the carburetor, checked the accelerator linkage, ensured proper timing advance, all the things you would expect to be culprits in this situation. You know what he didn’t check? The engine mounts. Why would you, right? Well, the true cause of this automotive haunting, as Scooby and the Gang might have sussed, was that a broken engine mount was allowing the motor to rock from the torque produced under initial throttle. That pressed the throttle linkage against the underside of the hood, opening the throttle further. Case closed.
That’s one weird case of cause and effect on a car problem, which is why it’s stuck with me all these years. Have you ever experienced, or have heard of, any that are weirder? Let us know.
Image: StudebakerInfo

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  1. 0A5599 Avatar

    The horn would honk at random times in the middle of the night, and stay honking until it was disconnected. I had no particular desire to diagnose it at 3am, but when I checked it after daybreak, it was back to normal. It might stay that way for a week or three, until the wee hours of another day, when I would be startled awake by a phantom horn honking in my driveway, which would once again be fine after dawn.
    The cause was the horn switch. It was constructed of two copper sheets separated by a thin insulator with a series of holes, and kept apart by a piece of foam rubber with a matching series of holes. It was intended that the driver would push anywhere in the center of the steering wheel, compressing the separating foam enough that the copper plates would make contact to complete the circuit.
    Instead, in the middle of the night, the air would cool off, dew would begin to form and the foam rubber would get just a bit soggy, weak, and conductive. Honk. The morning sun would burn off the dew. A new horn switch, and all was good.

    1. engineerd Avatar

      My Mustang had a similar issue. It turned out to be the hood switch for the alarm. The coolness of the night would cause things to contract and/or condense and the alarm would start going off in the middle of the night. A day at the friendly Ford dealer fixed it.

    2. ptschett Avatar

      My high school car, the ’73 Cougar, did that; one Sunday afternoon it decided to give us a horn concert. We pulled the horn fuse & left it that way for the remaining few years of its operational life.

  2. tonyola Avatar

    Back in the 1970s I had a friend who owned a Mitsubishi-built Dodge Colt. Whenever the driver’s seat belt was pulled out to its fullest extent, the dome light came on. We called it the sudden deceleration warning light.

  3. desmo Avatar

    Back in the 90s when my mum had her Beetle for the first time, she couldn´t start it. When she turned the ignition key, her Beetle wouldn´t do anything. Nothing. Reason was that she was used to manual Mercedes´ which could be started when the manual shifter was just pulled into “no gear” position without pedaling the clutch. Not so the Beetle. Ditto a manual shifter, the Beetles gearbox works so imprecisely that neutral position means nothing. Indeed it´s just an opinion. To be absolutely sure that a (parked) Beetle is in neutral mode you need to press the clutch additionally. Sometimes twice. Otherwise it won´t start. However: My mum called me on the phone to tell me her damn convertible wouldn´t start and I told her to switch to neutral pos. “I AM IN NEUTRAL” she yelled at me. Only when I came back a few days later I did figure out the error (which was a Beetle feature).

    1. wunno sev Avatar
      wunno sev

      i have never owned a manual car that didn’t need the clutch pressed to start. in addition, i have never owned a manual car that cared which gear i was in when trying to start.
      come to think of it, i don’t think any of my cars have had any sort of instrumentation to know which gear they were in. i think the oddity here is really the Mercedes’ behavior, and not the Beetle’s.

      1. caltemus Avatar

        My 1994 volvo doesnt have a clutch-interlock. Apparently volvo didnt do that until 1997

    2. Cool_Cadillac_Cat Avatar

      Neutral “safety” switch. It’s a simple switch above the clutch pedal.
      These have been around since at least 1972, because my mother’s Vega had one.
      Gear position is 100% irrelevant.
      They’re evil devices. However, jump with a paperclip, and it’s fixed forever.
      I have disabled every one in every manual transmission car I’ve ever owned immediately after purchase.

  4. Tanshanomi Avatar

    Had turn signals on a bike that wouldn’t work. I’d replaced all the bulbs, checked continuity of the wires, bench tested the flasher unit, and all were good. When I’d put it all together, no joy. Just about drove me mad. It turns out that I was flipping the flasher unit upside down on the workbench so the terminal blades were facing up. When it was installed in the bike, they faced down. It only malfunctioned in that orientation.

    1. dead_elvis, inc. Avatar
      dead_elvis, inc.


  5. autodafe20 Avatar

    I had the same problem with a 1965 Ford Falcon. Who knew a 170 ci could do a burnout. It’s not the throttle linkage pressing against the hood. The engine torque rotates the engine pulling the accelerator cable tight.

  6. 0A5599 Avatar

    I thought of another one.
    The Jeep had a failing battery. It was only holding 11.something volts. That was still enough to start the engine at a normal cranking speed, which masked the impending battery failure.
    However, when it was parked, and various power draws like the clock took the battery below some minimum threshold, one of the relays would fail to hold, and the HVAC blower would come on, and run until the battery was completely drained. Of course, hook up jumper cables, and the relay acted normally, as did the starter.
    It took a trip to the grocery store to figure out what was wrong. Gone long enough for the blower to come on, but short enough that it was still running.

  7. Citric Avatar

    Once, on a road trip when I was a kid, my mother’s ’98 Windstar suddenly shut down and wouldn’t restart. We were in the vicinity of the dealer where she bought it when this happened, so they looked at it, found some issue I don’t remember, fixed that and we moved on, before it happened again. Taking it back, they did a more thorough inspection and found the following:
    A mouse built a nest on top of the fuel pump. This resulted in the fuel pump overheating, which naturally lead to the van ceasing to move.

  8. The Real Number_Six Avatar
    The Real Number_Six

    Working as a lot jockey at a Chrysler dealer in the early nineties, two separate times I had to drive from Mississauga, Ontario to Hamilton Ontario on some kind of dubious errand for the dealership’s crooked owner. The first time I got to take a brand-new LeBaron Turbo convertible. It was a nice, sunny day and I naturally put the top down. On the way back, I hit a freeway expansion joint at whatever speed traffic was going, not anything fast. Suddenly there was a burning smell and smoke starting coming out of the glovebox. The radio and instrument panel went totally blank but the car kept going. I got back to the dealer, parked the car, and walked away. Someone tried to give me shit for breaking the car but I just played ignorant. A month or two later I went over the same expansion joint at the speed limit in a Chrysler minivan and the exact same thing happened…

  9. cronn Avatar

    A mid 80’s Nissan Bluebird automatic that would rev and accelerate by itself, a lot like the Avanti.
    The problem turned out to be a really nasty and greasy air filter that caused a vacuum in the carb somehow, causing the throttle to stick or even open even more by itself.

  10. Professor Lavahot Avatar
    Professor Lavahot

    In stop-and-go summer Texas traffic, a Saturn SC2 couldn’t get enough cooling air through its diminutive bumper intake to stay cool. You could turn the A/C on, which would force the A/C condenser fan to turn on, assisting the belabored radiator fan somewhat. Of course, the load created by the A/C compressor would just cause the engine to run hotter if left on.
    If traffic could only proceed, then airflow to the radiator would be sufficient for both my engine and my sweltering tissues to survive. But nope.
    So that’s why I’m sitting there, repeatedly turning the A/C on and off, leaning desperately out the window to listen for fan noise and A/C clicks, while the heater is on at full blast.

  11. JayP Avatar

    ’83 5000 – random coolant connector made from pot metal corroded into powder. Replaced it with a piece of turned aluminum. Months later when it came for time to use AC, didn’t work. I had no clue but pop remembered that connector had a wire connected to it. Replaced with the proper $60 part and it worked.

  12. Ross Ballot Avatar
    Ross Ballot

    I’ve been in multiple GMT800 trucks in which when you turn one way the HVAC system sends heat and when you turn the other it continues to blow cold air…cause/effect still unknown.

  13. Sean McMillan Avatar
    Sean McMillan

    I had a 72 Valiant that would kill a battery overnight. The battery tested good. I tried the usual tricks for hunting down current leakage and could not find any drain. Next day, dead battery. Put a kill switch in between battery and ignition. That solved it except for when I forgot to kill it, then I’d have to jump it in the morning. A few months later I got another car and took the Valiant back to my dad in NC. He never had the problem.He’d go weeks without starting and it would keep charge without ever using the kill switch.

  14. Scoutdude Avatar

    The motor mount breaking and causing unintened acceleration pretty well known, at least now. Millions of 60’s Chevrolets were recalled because of the fact that their mounts at the time did not incorperate a limiting mechanism that stops excessive movement when the rubber fails. So rather than replace the existing mounts with a properly engineered part the cars were outfitted with limiter cables. The bolted on with new longer exhaust manifold bolts and looped around the shaft for the upper control arm.
    The reason that the shifting engine caused the car to accelerate was the use of rods to control the throttle instead of a cable. Since the rod was attached to the linkage on the firewall or to the pedal through the firewall the change of the distance between that location and the carb caused the fixed length rod to open the carb. That of course caused the engine to torque more, increasing the throttle opening causing more torque and quickly enough a engine at WOT despite the fact that there was no pressure on the pedal.
    That certainly helped boost the change over to a cable in a sheath type of system which prevents the problem until the point where the cable is stretched so tight that the sheath breaks.

  15. Troggy Avatar

    I had a ’94 Fairmont. Whenever the dome light blew, the car wouldn’t start. For whatever reason, it was on the same circuit as the fuel injection.

  16. hubba Avatar

    Had a dime fall into the lighter socket. Took more than one fuse for me to actually look in the socket.

  17. William Robinson Avatar
    William Robinson

    When I was 15 years old my ma had a 84 topaz. One hot august night the car started and ran and turned on the headlights right outside my bedroom window. I went outside popped the hood and found the body ground to the battery had burned or corroded off. For the night I got a set of jumper cables and grounded out the battery to the strut mount and to the engine, the car shut off and didn’t bug me again that night. Next day we made a few new ground straps and it never happened again. Forken ol ferd

  18. Lokki Avatar

    Had an 88 Acura Interga -great car except that after I’d owned it a year it developed the weirdest problem either I or the Service Manager had ever seen. The car (a beautiful little aluminum DOHC with fuel injection) started perfectly on the first turn of the key, every time…. and then died. After a week of fussing around, the Service Manager called me and said the car was ready to pick up; they had essentially replaced the entire fuel injection system piece by piece unti they found the problem. I said, “great!” and went and picked up the car which started perfectly…and died instantly. They hadn’t found the problem after all, at least not when the car was outside in cold weather.
    After another week, the Service Manager finally called and very proudly told them they’d finally found the true cause. The ignition switch had failed some how, and when you inserted the key and turned it to “start”, it connected the contacts and the car fired up perfectly. However, the switch had internally cracked somehow and when you released the key after starting the car, the key didn’t move all the way back from the “start” position to the “run” position, so contact wasn’t made and the engine -having an incomplete electrical circuit -stopped.
    Replacing the ignition switch fixed the problem.

  19. salguod Avatar

    My Mazda3 would lose power steering and then the radio would turn off every time I used the turn signals. Turned out to be a bad ground creating a low voltage situation and causing the embedded systems to act goofy.
    My daughter’s Escort suddenly quit running. I checked the timing belt, changed the plugs and wires, checked fuel pressure and, I think, changed the knock sensor. After being told that the coil never fails, I finally pulled it to find it cracked open on the bottom. A check with the multimeter revealed that it was bad. Replaced it but it still wouldn’t start. Turned out that the bad coil sent a voltage spike to the ECU, frying it. A junkyard ECU finally fixed it.

  20. caltemus Avatar

    I went to turn off my 2001 outback one day, and the key wouldn’t come out of the cylinder. Brought it to a local ‘subaru specialist’ who told me that I’d need to replace the column which would be a whole mess, and just to deal with leaving the key in. I had keyless entry so it wasn’t a big deal to leave the key in. One day a few months later I go to hit the horn, and I get nothing. Upon further inspection the horn had blown. I used to have an 89 town car that had way better horns than the little japanese ones, so i had transplanted them behind the grill of the outback; the lincoln horns were of the spiral housing type, and i had to face the opening up for them to fit in the space. Turns out they had filled with water, which had then frozen, and shorted out the horn circuit when I hit the horn. Replaced the horn fuse and the key came right out.