Idle problem - Mixture screw wont help unfortunately.

[im]

I've developed an idling problem over the weekend. My Chim suddenly started idling at 2,000 rpm after idling perfectly at 1,000 rpm ever since I bought her.

I've turned the mixture screw all the way down till it wont turn anymore and it's still idling at 1,400 rpm. It's not jumping backwards and forwards (fluctuating between say 500 and 2,000 - its at 1,400 continuously.)

I've also tried another PH'ers technique of starting her up and letting her reach 90 degrees without touching the throttle and then turning her off - repeating this 3 times - but it didn't ehlp.

I'm baffled - could it be the stepper motor needs cleaning?

I think there was a thread on PH some time ago with pictures showing how to find, remove, clean and replace the stepper motor but PH's Search function can't find it. My Bible is also not much help as the photo's are faded in my copy.

Anyone got any ideas please?

[peebee]

Ian, the stepper motor is tucked just under the grill in front of the windscreen, just behind the plenum. It has a large hexagonal nut and an electrical plug in the end. You need to disconnect the plug and undo the motor using a large spanner, adjustable spanner or a mole grip or similar (but be careful because the motor is said to be quite susceptible to damage).

Take it out and clean the top of the motor using meths, WD40 or some other solvent. Also carefully clean the seating into which the motor fits using a clean cloth with the same solvent on it. Carefully refit the motor taking care not to cross thread or overtighten it.

You might also like to clean the butterfly in the air inlet pipe. This is accessible by removing the air inlet pipe from the plenum and opening the butterfly by manually pulling the accelerator cable from inside the engine bay.

Hope that helps solve your problems.

Peter

Edited by peebee on Sunday 18th March 17:05

[prtvr]

This link might help.

www.tvrcc-south-wales.co.uk/stepper.asp



Phil

[im]

Peebee & prtvr:

Thanks VERY much guys both Peebee's description and Prtvr's picture link are fantastic!

I should be able to do the job quite easily now thanks to you guys.

Your both stars.

im

[victormeldrew]

I don't think the stepper is actually that fragile, only if you try to use the plastic terminal housing to turn it. Use the 32mm hex and you will have no problems, just don't try to overtighten when you put it back. Don't forget the PTFE tape on the threads.