Idle issue & stepper motors

[RBatts]

Hi all,

My 7 recently failed to idle when starting up – it would simply cut out instantly unless I held the revs above ~1200rpm.
Myself and father-in-law started with dismantling the side of the throttle body, which revealed a small circuit board for the stepper motor with a wire broken from its solder. Quite relieved to find the problem early on in the disassembly; 7s thankfully offer supreme access to the engine bay. We held the loose wire back onto the circuit, turned on the ignition and could see a small plastic cam now rotate inside the housing, which pushes up a little bit of throttle i.e. the idle.

Evidently, someone had been here before as the solder work wasn’t factory. I later found record of the previous stepper motor repair in the log book – only now do I know what and where the stepper motor is.

Has anyone else had this issue with stepper motors? Is this unheard of?
It's re-soldered for now, but googling for a replacement part suggests this particular one comes from a classic Mini (Part No. JZX3062). Can anyone confirm?

Cheers,

Rob
1996 Roadsport 1.4 K-Series + Supersport kit

Edited December 4, 2023 by RBatts

[Jonathan Kay]

4 minutes ago, RBatts said:

Has anyone else had issues with stepper motors? Is this unheard of?

Previous discussions.

Jonathan

[OldAndrewE]

JZX3062 - Mini stepper motor for spi throttle assembly (minispares.com)

This is what that part number brings up

Note the comment on the Mini Spares site re idle problems

Edited December 4, 2023 by OldAndrewE

[RBatts]

Thanks OldAndrewE. That's hit the nail on the head:

"If you are having issues on idle then 1 or more of the 4 windings could not be working, this is usually due to corrosion or a soldered joint failing".

I shall shop around. Thanks.

[Englishmaninwales]

Really common problem on the 1400 SS idle control stepper. Broken solder joints on the circuit board and corroded TPS/stepper harness plugs plus the need (on my car) to shim the RHS engine mount to prevent the TB /stepper housing fouling the chassis tube.

I’ve been able to pick up complete TB/stepper units on eBay over the years.

[RBatts]

On 04/12/2023 at 16:43, OldAndrewE said:

JZX3062 - Mini stepper motor for spi throttle assembly (minispares.com)

 

After scouring the internet to find a replacement stepper motor, I took a bit of a gamble purchasing a complete throttle body from a Rover 214/414/200/R8 for just £40 (vs. the £180 quoted by Mini Spares). Different TB configuration, but from the shape of the housings it looked like it contained the internal components I'm after.
It arrived today and opened it up to find the exact stepper motor I needed, plus a spare cam for it too - ideal!

Edited December 21, 2023 by RBatts

[StevehS3]

An excellent find. More valuable information for Blatchat technical.