I fixed a problem with my accelerator pedal, which caused a different unexpected change to how my automatic behaves. Since it's my first automatic (I normally drive manuals), I want to know which is right between the old and new behaviour. I don't know if I fixed two problems, or fixed one and caused another.

Imagine you're driving an automatic at, for example, 34 mph on a flat smooth road. Imagine 30mph is around the speed below which you'd expect to feel this car downshift the gear. You ease off the accelerator pedal. Which of these would be the correct expected behaviour?

  1. The car should gently slow, downshifting gear without needing any brake, and keep on slowing. This is what my car did before.
  2. The car should gently slow to around 30mph, then stay in gear and cruise at 30mph. It shouldn't normally downshift unless you use the brake or the road changes (e.g. you go uphill). This is what it does now.
  3. There isn't really any right answer to this, it varies, either is fine, neither is cause for concern

Why I'm asking: While fixing a problem with my accelerator pedal sticking in my first ever automatic (which is also old and glitchy), having always driven manuals, its behaviour changed from 1 (downshifts when no pedals are used) above to 2 (usually doesn't downshift without using the brake). Since I've not driven any other automatic, I don't know if the new behaviour is normal or unusual - i.e. if I've made things better, worse, or neither.

What I did that seemingly fixed the sticking pedal problem was to replace the rubber boot on the throttle chain where it joins the accelerator pedal leaver, which had torn. It was supposed to be about 12mm of solid rubber rigidly holding the end of the throttle chain, instead, it was torn and spongey. I checked that the throttle chain is still slightly slack when the pedal is not pressed.

Driving feels very different now. The pedal had previously felt spongy (the torn rubber boot was getting squashed up before actually pulling the throttle chain) - but I'd just assumed automatics were designed like that to prevent excess acceleration. Now it's more responsive, which feels better.

The change I'm not sure is positive is: whereas before, at any speed I'd need to keep applying some gas to stay in a higher gear, and just leaving off the gas on flat would be enough to gently, slowly reduce speed and drop a gear (which I also assumed was a feature of an automatic), now, it drops speed until it reaches the point where it would normally change gear, then stays in that gear and maintains that speed (note that while the car has cruise control, it wasn't on and I never use it).

Having never driven any other automatic, I'm not sure if this is normal behaviour, and the previous behaviour was a fault caused by the knackered rubber boot making the throttle chain too slack, or if this is unusual behaviour, caused by my replacing the rubber boot making the throttle chain too tight.


I saw this similar question but a comment shows that it's a manual transmission (and seemingly they're stalling it, judging by how the engine cuts out...)

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    I'm not really sure what it is you're asking, but will say, when you pull your foot off the pedal, the vehicle should slow down. It sounds like your pedal and thus the throttle are not returning to a closed state. You need to figure out what's wrong and fix it. – Pᴀᴜʟsᴛᴇʀ2 Jul 31 '16 at 21:30
  • Okay, the original was a bit rambling. I've re-ordered it to put the actual question at the start! – user568458 Jul 31 '16 at 21:36
  • Your question is unclear. – Moab Jul 31 '16 at 21:52
  • @Moab I've editted it a lot to be clearer, can you be clearer about what about it is unclear? I'm not sure how to make it clearer than multiple choice with a detailed "why I'm asking" section and a link to a similar question that explains why mine is different – user568458 Jul 31 '16 at 21:55
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    I don't have the knowledge to make an authoritative answer, but anecdotally, the new behavior of your car is consistently the behavior of my '93 Olds when I drive it, but when others drive it the behavior alternates between the two (My definition of "no input" is a foot which is much more robotically still most). This leads me to believe that you fixed two problems, since pressure or grade changes still downshift. – newcoder Aug 1 '16 at 1:09

Couple of things to check: 1) Some transmissions had a 'down shift' cable. It basically monitored the throttle position and when you floored it it would potentially down shift. Many of these cables are adjustable. Check service manual for procedures. 2) On modern, electronic cars, I had a bad throttle position sensor. It told the computer the throttle was open double of what it actually was. So computer commanded a downshift all the time. Finally throttle position sensor completely failed.

Note the original throttle position sensor failed when the dealer did a "top engine cleaning" which included cleaning the throttle body. This in turn pushed dirt and crap in to the throttle position sensor. Learned my lesson.

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