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MG MGB GT V8 Factory Originals Technical - Idle stepper motor stuck?

In my continuous efforts to solve my erratic idle, I pulled off the stepper motor and housing for a clean up.

After the clean up and with the housing still off, I screwed the stepper motor back in the housing to see if the valve would seat. And it was a good 1/4" or more from seating. I thought this device was to remain closed (seated) until the computer told it to open. I've even tried to get the valve to open more, but it won't budge. So is my stepper motor stuck open? Or is this normal?

Question 2: I've also read in several archives about the GM stepper motor I can buy (if I need to). Does this plug in to my harness or do I have to modify the wiring?

Thanks for any help
Wally
Wally Jonker

Wally,

Are we talking Lucas/Bosch hot-wire system here ?

You should be able to hear the stepper motor whir when you switch on.

Do not try to force it, I've broken 2 this way !!! Just wash it out with carb cleaner, and lightly oil the thread .

Mike
M Barnfather

Mike,
Yes Rover 3.9L Hotwire EFi

Should I just plug it in and listen as I turn ignition on?

I thought I would be able to freely move the valve when the stepper motor was removed. But it doesn't budge.

With the stepper motor assembled to the housing and off the plenum, I can take a flashlight and look down the housing and see light out the other end. This shows me that it is not sealing. Is this a normal position for the stepper motor/housing to be in?

Thanks,
Wally
Wally Jonker

I initially blamed the stepper for my idle problems. It turned out that the throttle mechanism had got a knock at some stage and simply need to bent slightly back to where it should have been.
The proceedure is to temperaraly close off the stepper air line and then adjust the base idle.
Fine adjust- use the hex head screw on top of and just to the left of the throttle/butterfly valve. This may be closed off, unclose it.
Coarse adjust- bend the throttle stop plate.
Peter

Wally, IIRC you need electrical power to move the stepper motor.

Several steps in the Base Idle Speed Adjustment pertain to the stepper motor. Going through this procedure should tell you whether its working or not.

Good luck,

***************************************
With the engine at operating temperature and an accurate tachometer connected:

Center punch and drill (1/8" bit) the tamper proof plug located on the throttle housing.

Remove the plug with a sheetmetal screw and pliers.

Discard the plug and clean up any metal chips.

Switch the ignition on - DO NOT START THE VEHICLE.

Disconnect the stepper motor plug

Switch ignition off

Listen for click from EFI main relay (under the right front seat).

Reconnect the stepper motor plug.

Switch the ignition on - DO NOT START THE VEHICLE.

Disconnect the stepper motor plug.

Start the vehicle in neutral without touching the accelerator

Adjust the base idle speed with a 3/16" Hex wrench to 550 to 650 RPM by turning the base idle screw. Turning counter clockwise will raise the speed and vice versa.

Reconnect stepper motor plug.

Switch ignition off.

WAIT for main relay click

Switch ignition on, start the engine and rev briefly to 2000 RPM

Idle speed should stabilize at 665-735 RPM

Install new tamper proof plug.
Edd Weninger

Fast version:
1) Turn off motor and leave stepper motor plugged in
2) remove hose from plenum where th stepper motor attaches
3) put ductape over fitting and reattach hose (sealing it, and the plenum from each other).
4) Start the motor and adjust the idle speed screw to get a nice smooth idle
5) shut off motor, remove tape
6) reattach hose
7) Start motor and drive off happy.

It's nothing more than a GM stepper motor, and there are no wiring changes to make it work. Just plugs right in.

Air leaks will cause idle problems, so will plugging things into the wrong plugs (i.e. the water temp sensor and the fuel injector right next to it).

Justin

Thanks to all for the replys.

I'm going to have someone turn the ignition on while I actually look at, and hold, the stepper motor (while plugged in to the harness) just to make sure that it is working. I want to eliminate the possibility that it is not working. (Worse case, I buy a new one anyways!)

Then I will check/adjust the base idle...(I read Justin's archive from last May and have it printed and filed!..Thanks:)

And I also remember screwing with the Throttle Position Sensor a long time ago. So I also need to re-adjust that with the meter back to where it belongs.

I also just bought a new Temp coolant sensor... and I'm positive everything is plugged in to the right spot. So after I do these other adjustments, maybe then I will have a smooth idle!

Again, thanks to all who replied!

Wally

Wally Jonker

Hey Wally, That is why they call em "idle stepper"s--they are lazy and always get stuck.
James Johanski

This thread was discussed between 23/04/2006 and 25/04/2006

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