is it possible to get rid of the stepper motor

[snorky]

with the wanky way the stepper works ie: revs all over the shop then settles after a few seconds . Is it possible to remove it from the scheme of things ? none of my other cars had these motors and idled perfectly fine without one.....why do we need it?

[GreenV8S]

You don't need to have one, it just helps maintain a consistent idle speed in all conditions. Without one, the engine may need a little help to keep running for the first few seconds on cold days, and will idle slightly slower than normal until it warms up, and the idle speed will vary a little as you switch the lights and aircon on and so on. But if you just disconnect the electrical plug once it is idling happily at the right speed, it works fine. Or remove the stepper motor completely and either put a fixed restriction in its place, or blank off the bypass hose and set the base idle adjuster to give you your idle. Or do what I did, and replace the manifold/plenum setup with one that doesn't have any provision at all for an idle control valve. It works fine, and imo if you have idle stability problems it's worth disconnecting it temporarily just to see whether it is something that the stepper motor is provoking, or an underlying air/fuel/ignition fault.

[snorky]

hmmm interesting...mine is working but I hate the bit where it stays at 2K revs then the stepper actually moves and the revs drop to idle....

[sparkythecat]

GreenV8S said:

You don't need to have one, it just helps maintain a consistent idle speed in all conditions. Without one, the engine may need a little help to keep running for the first few seconds on cold days, and will idle slightly slower than normal until it warms up, and the idle speed will vary a little as you switch the lights and aircon on and so on. But if you just disconnect the electrical plug once it is idling happily at the right speed, it works fine. Or remove the stepper motor completely and either put a fixed restriction in its place, or blank off the bypass hose and set the base idle adjuster to give you your idle. Or do what I did, and replace the manifold/plenum setup with one that doesn't have any provision at all for an idle control valve. It works fine, and imo if you have idle stability problems it's worth disconnecting it temporarily just to see whether it is something that the stepper motor is provoking, or an underlying air/fuel/ignition fault.

Just elaborate on that for us thickies would you Pete?
I (like others) accidentally snapped my stepper motor off in the plenum in France last year. I managed to make a blanking plug from plumbing fittings, but I couln't get the b@st@rd thing to idle. Whilst I've no intention of repeating the experience, a get you home fix would be handy to know

Edited by sparkythecat on Friday 27th October 18:36

[brummiewedge]

I dont run mine. Just blanked the bypass. You just need to spend a few seconds in the morning to get it to idle. Getting it out the garage is enough. Ditch it!

[tvrbob]

You could choose to run on V Power (Optimax) then your problems would be over. My stepper motor pi55ed me off something awful for the first couple of years, cleaning every other month or so. Then I discovered that using Optimax meant no more carbon build up. It'll be more than 15k since I last had the stepper out.

In-fuel detergent keeps the stepper motor clean

[overhere]

I have to say, I run regular unleaded (Tesco, Sainsbury, joe bolgs) and the car runs great all the time, I've never had any problems with idle except 50 miles after putting STP injector cleaner in, it revved to high for a while at idle but then was ok after a day or two. I've seen subjects on this forum about how anything but Optimax (V Power now) or Texico whatever makes the car run crap and how you can feel the difference between...

I do put V Power in for track days or when I'm out for a thrash but to be honest she's happy whatever I put in her. Maybe I'm just luck but I laugh when I hear the arguments. If she runs great on the cheap stuff why waist the money?

[GreenV8S]

sparkythecat said:

set the base idle adjuster to give you your idle.

Just elaborate on that for us thickies would you Pete?
I (like others) accidentally snapped my stepper motor off in the plenum in France last year. I managed to make a blanking plug from plumbing fittings, but I couln't get the b@st@rd thing to idle. Whilst I've no intention of repeating the experience, a get you home fix would be handy to know
[/quote]

I wasn't really thinking of this as a get-you-home fix for a broken off stepper motor, but if that happened what I'd do is squash the bypass hose to block it off, seal off the exposed opening into the plenum where the stepper motor would normally go (half a dozen layers of gaffer tape should do the trick, something rigid over the hole to stop the tape being sucked in would be even nicer. This would mean you're left running on the base idle which is typically around 500 rpm and too low to be usable, so either jack the throttle open or (better) wind trhe base idle screw out a few turns until the engine idles at something approaching a sensible rpm. The base idle screw is visible on the top of the throttle housing close to the point where the intake hose attaches. It originally have been covered by an anti-tamper plug but these are usually discarded.

[That Daddy]

if your that bothered about fast idle in the morning,ie cutting out & overfueling woes,just fit a K bosch jetronic air bypass valve into the plenum,little bit of wiring manages itself,ford capri/escort/orion/granada/VW golfs/VOLVO etc,it fact one of these cars also uses a bypass screw on the unit so if you are unable to wind out the rover screw enough to get your base idle then you can use the bosch one,this removes the problem of moving the butterfly and upsetting the TPS switch settings.Oh this unit is much more reliable than stepper unit, just having a moving window that works on an heating element to allow more air to pass when cold.this may be of no use but its an option,easily found s/hand and cheap.

[GreenV8S]

That Daddy said:

this removes the problem of moving the butterfly and upsetting the TPS switch settings.

Just for reference, the base idle adjuster is a screw that regulates an internal bypass within the throttle body, it is separate to the adjustable throttle stop. Adjusting the base idle won't affect the TPS settings.

[That Daddy]

no GREEN V8S, what i was saying was if the idle bypass on the throttle b/fly did not pass enough air then the bypass mod could,i know the air screw does not affect the tps position,but some would consider adjusting the b/fly to up the engine speed,thanks anyways.

[tahiti450]

tvrbob said:

...........Then I discovered that using Optimax meant no more carbon build up............. In-fuel detergent keeps the stepper motor clean

Just puzzled as to why the stepper motor piston would come into contact with significant quantities of fuel, since this is injected way downstream at the back of the inlet valve??? As i see it the deposits in the plenum and inlet tract come from the crankcase via the breather system.

[GreenV8S]

At low speed and low throttle openings, you get exhaust gases sucked back into the plenum as far as the throttle plate. You could think of it as mostly exhaust diluted with a bit of fresh air. The exhaust gases being sucked out pull fuel with them (plus soot etc from the exhaust).

[tvrbob]

tahiti450 said:

tvrbob said:

...........Then I discovered that using Optimax meant no more carbon build up............. In-fuel detergent keeps the stepper motor clean

Just puzzled as to why the stepper motor piston would come into contact with significant quantities of fuel, since this is injected way downstream at the back of the inlet valve??? As i see it the deposits in the plenum and inlet tract come from the crankcase via the breather system.

I've never thought to question this. I had stepper motor problems and was advised by the PH collective to stick to Optimax to remove the issue. Having found that this worked and then having it reconfirmed by the problem reappearing during a UK tour during which I had to use a variety of high octane fuels. On my return I cleaned the stepper and reverted to Optimax and the issue went away again. I don't pretend to know why but I do have faith that it works.

[TVR keith]

So is this a valid reason to only use large throttle openings?

[brummiewedge]

I tried mine this morning with no gas on the pedal, cos i was leaning in through the window jumping from my Passat ( flat battery see.). It started and idled from cold and i have NO stepper motor. It used to drive me wild in traffic with that when it feels like ticking over at something normal type thing. Really guys do away with it.

[andy-w]

I take it you disconnect the stepper motor when it idles nicely and the engine is still running?

[brummiewedge]

Its not disconnected, but taken out of the air bypass system, just put a bung in the pipe. Also around 1.8%CO at idle which on mine is 900ish rpm. Both hot.

[GreenV8S]

I meant disconnect the electrical plug while leaving the stepper screwed into the plenum, as a way to temporarily disable the stepper and see whether it is contributing to idle stability problems. There's no great harm in leaving it like this permanently, if you like. Or replace the stepper with a fixed restriction. Or remove the air bypass hose and block both ends. Yes, unplug while the engine is running (the ECU will 'park' the stepper motor when you switch off.

[andy-w]

Thats what i was thinking...if you turn the engine off the stepper motor goes back to its start position. Might give it a go on my way home tonight...se if it makes any difference. Mindless curiosity more than anything else!!!