Bodged Stepper Motor

[angus99]

I've now had my chim for a couple of weeks and have a short list of jobs to do. first on the list (and I thought easiest) was to clean the stepper motor, to try and improve idle speed problems. So I disconnected the Electric comnnector and then noticed that the Stepper motor body was tie wrapped to what looks like the throttle cable. It appears that the unit has sheared at the plenum chamber. A previous owner must have re-inserted the unit sealed it with some gunk and tie wrapped it to the cable for added support. I've tried to re-start the car and it seems to work ok, however there is quite a bit of air now escaping from the plenum chamber. I therefore have a couple of questions.

1) where to get a new part / is it a standard rover part?
2) How do I get the sheared bit out of the plenum chamber
3) Will driving the car risk any further damage? (I need to run the car because my daily car is in for a new Clutch after only 3000 Miles from new!!!)

[GreenV8S]

angus99 said:

1) where to get a new part / is it a standard rover part?
2) How do I get the sheared bit out of the plenum chamber
3) Will driving the car risk any further damage? (I need to run the car because my daily car is in for a new Clutch after only 3000 Miles from new!!!)

It's a standard Land Rover part (Range Rover 3.9).
You will have to unscrew it by hand.
You will need to get it sealed reasonably well otherwise the un-metered air will make the engine run lean and may eventually put the ECU into a strop. Make absolutely sure there's no possible way for anything you use to seal it to come loose and get sucked into the engine.

[Cider Andy]

angus99 said:

How do I get the sheared bit out of the plenum chamber?

It's only plastic and as it's sheared it shouldn't be very tight. Not knowing what the inside of the sheared part looks like, I'd guess at trying to gently wedge a flat screwdriver blade in it to unscrew it, if it can't be turned by hand.

[angus99]

Drove in to work this moring with the stepper motor removed and the car seems to run a lot better. i.e. started up beter from cold and the idle spead is much less eratic. May be a stupid question but just wondered If i Really need to replace the stepper motor or whether I could just blank of the hole in the plenum chamber.

[davidlscott]

I managed to snap mine last year right at the edge of the plenum and couldn't get it out.
My local dealer told me to wrap it up with tape and I thought it ran better without when I took it to them (about 15 miles).

They didn't charge much over the cost of the new motor to fit it but you need a decent bit of expertise to get the broken bit out and I was in such a strop after breaking it that I didn't dare do it myself.

[GreenV8S]

angus99 said:

Drove in to work this moring with the stepper motor removed and the car seems to run a lot better. i.e. started up beter from cold and the idle spead is much less eratic. May be a stupid question but just wondered If i Really need to replace the stepper motor or whether I could just blank of the hole in the plenum chamber.

You don't actually need the stepper motor, personally I think they're more trouble than they're worth, but be aware that this is the only idle speed control you have and without it the idle speed will vary depending how hot the engine is, what electrics you have switched on etc. You may have to help it with the throttle for the first few minutes on cold days.

[andy-w]

[quote=GreenV8S][quote=angus99]Drove in to work this moring with the stepper motor removed and the car seems to run a lot better. quote]

You don't actually need the stepper motor.quote]

I had had mine disconnected for a few months now and have never had any problem with irratic revving, high or low tickover and the car seems to run smoother in traffic. All i did was get the car up to temp so it was ticking over at about 1k revs and then pulled the plug...plus it is one less thing to eliminate if you do have a problem.

[GreenV8S]

andy-w said:

[quote=GreenV8S][quote=angus99]Drove in to work this moring with the stepper motor removed and the car seems to run a lot better. quote]

You don't actually need the stepper motor.quote]

I had had mine disconnected for a few months now and have never had any problem with irratic revving, high or low tickover and the car seems to run smoother in traffic. All i did was get the car up to temp so it was ticking over at about 1k revs and then pulled the plug...plus it is one less thing to eliminate if you do have a problem.

Some people have said that the stepper motor seems to have moved after a while, perhaps from the vibration. If you're sure you want to do away with it permanently it would be worth blocking the bypass hose and adjusting the base idle up to take the stepper motor right out of the equation.

[andy-w]

That was kind of one of the mods i was going to do when i had the engine out...i was going to get another plenum and make a twin plenum with the second intake on the opposite side to the existing one so i would have to lose the stepper anyway.

[occasionaluse]

just a quick question - i had a look at my stepper motor and was so careful taking it out - but then on inspection it is not plastic at all - some sort of alloy and very strong - is this standard or aftermarket?

[sparkythecat]

The threaded bit is alloy but it's not as strong as it looks. Snapping it off in the plenum is relatively easy. Installing a stepper motor is the only job I can think of where being limp-wristed is a definite advantage

[The AJP Griff]

occasionaluse said:

just a quick question - i had a look at my stepper motor and was so careful taking it out - but then on inspection it is not plastic at all - some sort of alloy and very strong - is this standard or aftermarket?

Perfectly normal,they are alloy,maybe some are also plastic,but i've never seen one?If one sheares off,you can easily replace just it's housing,rather than worry about the plenum as a whole

[angus99]

well got back from work and decided to try and remove the threaded bit from them plenum. came out ok with a large screwdriver head from my socket set. But with the housing blocked off the car now revs to about 2700 rpm at idle. unblocked the car stalls.

I've ordered a new stepper motor from MM 4X4 (£54 +vat), but it looks like I'll have to wait for this to arrive before I can use the car. Unless there is a way to adjust the idle speed without the stepper motor installed. any ideas?

The subaru is still in getting the clutch fixed so bopth cars now off the road!

[GreenV8S]

angus99 said:

Unless there is a way to adjust the idle speed without the stepper motor installed. any ideas?

The idle speed is determined by the throttle stop, base idle adjuster and stepper motor. You want to leave the throttle stop well alone. That leaves the base idle adjuster on the throttle body, and the air bypass via the stepper motor. With the stepper motor removed the air bypass is effectively fully open. You can restrict air through it by restricting or blocking the hose to it. If you block the hose completely the engine will be running purely on the base idle setting, which if it is set correctly will correspond to about 500 rpm which is far too low. So you need to either partially block the bypass hose, or fully block it and then wind the base idle up a bit.

[angus99]

Tried blocking off the Plenum housing and adjusting the idle controller as I though this would have the same effect as blocking the bypass hose. Got the revs down to about 1500 RPM at idle but then noticed that the exhaust manifolds were glowing red which was a bit scary. Not sure if this is unburnt fuel gatting in to the mainfold but I think I'll leave it alone untill the new stepper motor arrives.