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Cleaning the stepper motor
Paul Clark posted a query on the V8BB seeking help on erratic running and how to clean the stepper motor. The V8BB postings are recorded here for future reference plus a note on how to clean the stepper motor and points to other causes of erratic running that might need investigation. (Apr 08)

Paul Clark posted a query on the V8BB in March saying "my RV8 drinks petrol, struggled through the emissions test at the last MOT and examination of the spark plugs confirms it is running 'rich'. I'm told that the stepper motor is likely to be 'carboned' up but cannot find any notes or diagrams explaining how to go about putting this right. The car is standard an a Japanese import. Anyone have this information?"

Geoff King responded: "the stepper motor is on the right rear of the plenum chamber. It adjusts airflow bypassing the throttle disc for idle speed control and is unlikely to have a significant affect on fuel consumption or emissions – idle mixture is adjusted on the air flow meter. A faulty temperature sensor, worn injectors or a problem with the cats could cause poor fuel consumption". He added "I doubt if the stepper motor is the (only) problem. It sounds more likely to be a fault with the coolant temperature circuit causing the ECU to think that the engine is cold and requiring a rich mixture. The stepper motor is trying to maintain the idle speed by allowing more air to by-pass the throttle disc but the engine will be rough and use excessive fuel".
What does the stepper motor do?
The stepper motor adjusts airflow bypassing the throttle disc for idle speed control. With erratic idle, the stepper motor is normally the first suspect, as it can get fouled up with carbon, and may need a clean. The idle control is a fairly crude affair, utilising an air bypass screw (called the base idle setting) and a simple stepper motor controlled air valve to keep the idle steady as the engine loads vary.

Where is the stepper motor?
The stepper motor is on the right rear of the plenum chamber.


How do you clean the stepper motor to remove carbon deposits?
To clean simply disconnect the electrical connector and unscrew the stepper motor from the plenum chamber. Cleaning with WD40 or white spirit or meths used sparingly is a 10 minute job.
Paul Clark was pleased with the feedback he received on the V8BB and added " The RV8 does sit at a high idle speed often and of late runs roughly at idle like a car with a manual choke left out too much. I have checked the manifold bolts and they seem OK. I have purchased the A/R black tube but have yet to build up the confidence to do the re-timing, also need the weather to warm up!"Rob Collier noted: "Regarding the rough running. Make sure that you have changed both the fuel filters and that the air cleaners is clean and have changed the spark plugs. I also used some Forte petrol treatment to clean the fuel system (Clive Wheatley sells it) and my car ran noticeably better after using it".
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