Jerking sensation at low revs

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JDX
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Jerking sensation at low revs

Wed Sep 02, 2020 3:36 pm

Hi,
I have recently noticed at low revs (around 1-1.5k) usually when slowly pulling away or in slow moving traffic (i.e. gentle acceleration), there's a stuttering / jerking feeling and slight knocking sound. I have limited technical knowledge, but it feels like it's either not quite in gear or not firing right i.e. imagine the opposite of 'smooth' pulling away. It's almost like you're driving over tiny bumps in the road. It doesn't always happen.
Does anyone have an idea what this could be, or if it's a known issue?
Thanks a lot
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Re: Jerking sensation at low revs

Wed Sep 02, 2020 3:49 pm

Does it get any worse if you are on full lock? There is a known condition at low speeds, usually at full (or near full) lock that is frequently a result of the car not being fitted with either the correct tyres, or having tyre wear differences of more than 1.5mm between the axles (or any one tyre compared to others).

It often appears in cars with staggered wheel sizes and is generated by different rolling radii ‘winding up’ the diffs or transfer box. Sometime a grumbling or grinding noise is also apparent. It’s more common on earlier variants than yours though.

Because the staggered tyre sizes can result in different circumferences, there are matched sets with the tyres for BMW marked with a ‘*’ on the sidewall. Audi, Merc and other car manufacturers have their own tested and approved version (AO, MO, MOE).

Low tyre pressure in one wheel can also cause this.

If not this then it could be worn fuel injectors, gearbox fluid levels, transfer box, air mass sensor and a host of other possible causes. You may need an error code readout doing to see if anything shows up. Chasing these odd problems down can be tricky so a code read might narrow the scope.
:ant: Never anthropomorphise computers. They hate that.

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