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Revs dropping in 2007 KX-S


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I have a Nov 2007 KX-S with 38000km on the clock & I'm wondering if anyone else has experienced or knows what could be causing the following:

- Sometimes when braking, the car actually surges forward briefly before slowing (somewhat disconcerting!)

- Whilst driving, the tacho makes very sudden changes. The other day, it dropped from about 2.5k to 1.5k revs in a fraction of a second. Other times, it suddenly jumps up say 500 revs. Rather erratic. This does not seem to coincide with gear changes & there's not always a noticeable drop/gain in power.

- Sometimes driving seems effortless, whereas other times it feels like the tyres are flat or the brake's on or just otherwise labouring & sluggish.

Fuel line? Accelerator cable? There doesn't seem to be much difference after a service, but the problems seem to be becoming more frequent. Just frustrating that they can't always be replicated - more a knowing it's not "normal".

Any clues?

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Hello gemiNy - I can help with some of your questions.

I occasionally notice surging when braking, but it always corresponds to the gearbox changing to a higher gear for whatever reason it's electronic brain thinks is right. Never could work out a reason this would happen, but yes it does feel like the car is running away slightly before the brakes start to slow it

Those very quick rev changes I believe are when the torque converter "locks up" and that is why you do not notice it corresponding with any discernable gear changes. Perfectly normal behaviour. In undulating country the revs will drop and jump back up quite a lot, especially when on cruise control.

As for the sluggish behaviour - I only notice it when the car is cold. This too is perfectly normal as the engine is regulated to only low revs between gear changes until everything is at normal operating temperature. Even if you press the accelerator to the floor, the electronics will not let the engine perform fully, and cause those symptoms you describe.

However if you are noticing a change in all this behaviour, it could very well mean that something is wrong :(

Hope that helps, and more importantly that it makes sense!


Edited by holmesie
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Any clues?

Faulty "snow" button could be the cause of the sluggishness.

Holmsie is correct re the lock-up torque converter; drops revs by about 400 as it locks. On cruise control, a slight hill will cause it to unlock, thereby increasing the revs by 400. (in fifth).

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