Changes by last author:
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Part number: TVR E0121 (Other Rover part numbers exist for the same part)
The tapered end of the plunger moves in and out from the motor to open and close the idle valve. The motor itself screws in to a housing. The taper is not the sort that should really cause stickiness (it's too shallow) but something is causing issue - it may be something internal to the motor causing the problem when it driven to extend the plunger too far. |
| I agree it's not at all a good design of idle valve, but it is the standard part for this car so I'd like it to work if possible. It is impossible to see what is happening when the stepper motor is assembled in the housing so I only have a theory that it sticks - however it does fit the facts I have found so far. |
| I am assembling a collection of VEMS logs now that should show different behaviour for the same apparent IAC position. It's not obvious from one VEMSLOG that there is any problem because it can be made to work for that particular IAC position, but on restart it is different. |
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The stepper motor itself has a useful range of 180 steps. In "standard direction" mode I configured the minimum steps to 80 and maximum steps to 255. This demonstrates the "sticking" problem. With the stepper operating direction reversed, I configured minimum steps to 0 and maximum steps to 175. There is no evidence of the sticking problem probably because the stepper does not need to operate near the fully closed end stop. It should be noted that the standard ECU uses the "valve fully open" end to reference the stepper. It sends 200 pulses to drive it during start up. |