When the throttle jams…

Posted on August 30th, 2007 in Opinion,Safety by Julian Edgar

skidmarks.jpgHaving the throttle jam fully open is a pretty exciting idea. And an even more exciting reality.

I’ve had the throttle jam fully open twice in my driving career.  Once it was in city traffic, in second gear.  I’d just had the throttle body-to-plenum rubber hose off, and when I’d replaced it I hadn’t orientated the hose clamps the right way around.  The result was that when the throttle lever moved past the clamp screw it couldn’t get back: instant sustained Wide Open Throttle. 

After thinking “Shit!” I turned off the ignition key and then swapped lanes to the curb.

The second time was more dramatic.  At a balls-to-the-wall 180 km/h in my tiny 660cc turbo Daihatsu Mira, I lifted off, but the car kept going hard.  Standing on the brakes worked well, and then I switched off the ignition.  Bit nasty, though – switching off a turbo car at full throttle….  That time the water/air intercooler had blown off its mounts, in the process jamming the throttle.

I’ve also been the passenger in a car when the throttle stuck. We were on a back road, doing 0-100 km/h performance times, when the driver suddenly exclaimed in consternation. Before I could ask the question, the car was bouncing off its rev limiter and I guessed the cause.

When it happens, it happens quickly.  Best is to stand on the brakes and then switch off the ignition – but only to the extent that kills the engine.  Other approaches include knocking the gear lever into neutral and then hitting the key, or even – in desperation – yanking on the handbrake as well. 

Once I lived in a house facing the upcoming axis of a T-intersection. When we looked at buying the house, my then girlfriend (and now wife) said: “What if someone loses their brakes? They’d come roaring straight into the house.” I looked at the situation, saw the steep embankment they’d have to cross to reach the house and scoffed at the idea.

So we bought the house.

When the bloke drove his Falcon two-door up the gutter, across the footpath, through some hefty bushes, up the two metre rise, through my veranda post, and then finally into the front wall of my house, I was a bit taken aback. Especially since he only carried out only the first step in the throttle-jammed scenario – standing on the brakes.  The skid marks left by the front wheels were more than 30 metres long….

But the best cure is prevention – whenever you’ve been working on anything around the throttle, before you shut the bonnet it pays take a step back and look at the situation. Is there anything that could jam the butterfly open?

It’s a pretty vital question for anyone working on cars…

8 Responses to 'When the throttle jams…'

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  1. Mark said,

    on August 30th, 2007 at 8:01 am

    Yep, it’s certainly a wild ride… I learnt to drive on a motocross track in an old VW Beetle about 20 years ago. I was bumping down the back straight (I was about 12 years old) only to find the throttle stuck wide open and a 180-degree corner approaching rapidly. I stood on the brakes (without much luck in a ’58 beetle) then hit the kill switch. I ended up skidding over the back of the banked corner and flattening a few bushes – I thought it was great fun!

    Unfortunately that was not the last time it occurred – those Beetle throttles had a habit of jamming when bouncing over REALLY rough ground. It was never quite as exiting as the first time though.

  2. Chris said,

    on August 30th, 2007 at 11:09 am

    It can be very wild.

    I was 18, had just recieved my blacks and finished working on an old 86′ Magna. The second drive out i decided to give it a squirt, but the squrt never ended.
    I found my self traveling down hill on an 80Km/hr rd. Standing on the brakes worked… till they faded.
    Switching off the car and throwing it into neutral worked sort of. I think the engine was overheating by that time so hotspots in the cylinder keped it ticking over in a lurching kind of rumble. 5 mins later it was off.

    The cause? The throtle cable had picked up dust on the exposed end. Previous owner, elderly lady never used full throtle. I did!

  3. Leon said,

    on August 30th, 2007 at 12:38 pm

    Yes it is exciting! but fellow road users do tend to look at you a bit funny… Its happened to me a few times. Dodgy throttle return spring on the ol’ 76′ B1600 mazda ‘u bute’ ute, no serious problem just clutch, brakes, curb.

    However the 83 Alfa GTV6 was a different story…not so fun, more scarry and requiring much faster reacton to avert major disaster. A bracket in the throttle assembly was interfering with another component causing it to get stock wide open and this was induced by work done earlier. Moral is, check before you drive!

    Hopefully I will be more careful with the R32 GTR because based on previous experience this would be much harder to ‘catch’ in time…

  4. Jerry said,

    on August 30th, 2007 at 9:40 pm

    Yup…been there have the T shirt. My Aztek had cruise control problems…It would not turn off and when I braked it thought I was going up hill so it would try to accelerate to maintain speed. First time was with the family on an open highway. Second time was on a highway coming up to traffic…..3rd time ….month later was in the city coming up to a red trafiic light.

    Nobody took me seriously until I dropped the car off at the GM dealership and “gave it back”. Left my buiness card and told GM the car is theirs until they solve the problem. EVERONES safety was not worth it.

    An hour later I received a call. They found the problem. A small locking ring holding the cable onto a bracket came loose. Every so often it would slide down the cable far enough to jam under the throttle pulley.

    Anyway fun it wasnt if it ever happens again I will insist they take me more seriously the first time.

    Thankfuly my track experience kepy me calm and prevented incident. …..I turn off the ignition. But when I share this with people, most are horrified and ask how on earth did you manage to stop!

    Which brings another issue to hand…driver training and education. Very few had thought that turning off the ignition would have been a solution if it happened to them!


  5. Chris said,

    on September 1st, 2007 at 10:32 am

    Its a scary baptism of fire alright – a few years ago I replaced the air filters in my V12 Jaguar with K&Ns – it went in for a service and it would seem the mechanic pulled the pair out, looked at them and replaced them – back to front. With the bulky side of the air filter now sticking inwards, both throttle blades caught at about 3/4 throttle, while I was turning right across a major intersection in 3 lanes of traffic. The resultant powerslide as I panicked and then turned off the ignition almost took out two lanes of traffic, slammed the car sideways into the curb (cracking both wheels)…and a serious brown-trousers moment!

  6. Kieran said,

    on September 2nd, 2007 at 6:22 pm

    I had the same problem with a Morris Mini 850. It was a throttle return spring which was seated wrongly and unhooked itself. It happened once in a McDonalds carpark, and once at a major suburban Adelaide intersection. Luckily, it happened on a green light and I was at the front of the queue. That mini never took off so quickly in it’s life! I was turning a corner, so I changed gears once or twice to keep up with the revs and then switched off and pulled over. A scary experience for an 18 year old in busy traffic!

  7. Jack said,

    on September 4th, 2007 at 11:31 am

    It happened to me in a Peugeot 205 GTI with a 160bhp 16v engine, I was flat to the floor in 3rd when the BMW 5 series in front of me backed off and when I did the same the pug kept going, fortunately I had room for some swift overtaking and then a stab of the throttle pedal released it again. In this case it was caused by the top of the pedal getting stuck in the bulkhead soundproofing after the carpet had been removed.

    “But the best cure is prevention – whenever you’ve been working on anything around the throttle, before you shut the bonnet it pays take a step back and look at the situation. Is there anything that could jam the butterfly open?”

    The same goes for the pedal end too!

  8. Dave said,

    on November 12th, 2009 at 4:48 pm

    happened to me once also, though this was on my bike.

    wasnt nearly as dramatic as most of these stories. i went for a gear change to over take, opened her up, then let go to shift, pulled in the clutch, and the engine overrevved. was a boring (but safe) experience. luckily the engine only needed a $10 valve clearance adjusting screw from the wreckers to fix the problem.