stepper motor... how exactly does it work?

[TVR Beaver]

How exactly does the stepper motor work?
Reason I ask is that I get a bit of ‘missing’.. or ‘hesitance’ when driving in 4th at 30 mph or about 1200 / 1500 RPM…. So just when you put the first bit of pressure on the loud pedal and the butterfly starts to open. I did read on here that a guy had improved shunting by fitting a central heating tap to the stepper motor feed pipe and adjusting its flow so thought I’d try it.. So I’ve fitted an in-line tap and messed about with it for a bit.
It’s set to about a 4mm hole now and for sure it appears to make things better. Not had time to fully close it off and see what that does now its warm and it looks like we are in for a thunder storm so won’t be out again tonight! I suppose the only problem will be starting from cold as it won’t work as it should and I’ll have to hold it on the pedal until it warms up a bit so it will tick over…
Anyway… back to the original question… how does the stepper motor work?
I’d assumed it opens when cold and then fully closes when warm… but doing what I’ve done suggests otherwise… can it or does it still open a bit when warm to help tickover?...
So if this helps my problem, is it opening too much when warm (if it’s meant to do that) and if so, why.. what controls how much it opens (ECU I guess)… or is my unit over the hill and needing replacement?. I’ve done the usual cleaning… even taken the point out and polished it in my lathe… and cleaned the seat etc….
Any thoughts would be useful… cheers

[2Munkys]

A bit from Mark at Blitzracing (he posts on here). Have a shufty:

http://www.g33.co.uk/fuel_injection.htm

[TVR Beaver]

Thanks Bruce... will have a read tonight... see if it explains what it does...

[blitzracing]

The stepper should not really come into play when the car is moving, as the speed sensor signal signal to the ECU disables it. The reason for its existance is to provide a extra air when the engine is cold, and control the idle when the engine is subject to different loads, like air con or when the fans switch on (loading the alternator). I think you are experiancing the dreaded "shunting" that tuned Rover V8's suffer from, that can be down to poor fueling, ignition / timing or even plenum design with certain camshafts.

[TVR Beaver]

Hi Mark... it's not real shunting... it's just a bit hesitant sometimes when you are on very very light trottle.. I now have the 885 cam fitted with a 72mm plenum and ali 45mm trumpett's onto a ported manifould... It's not bad.. just the odd miss or poor fire every so often... but random so it's not related to a cylinder ect, more slow air flow or something...
Rob at V8D could not put his finger on it.... I changed my 90 deg hose to the plenum as the one fitted was very tight.. the new one has a better rad on it and this made an improvement.. but it's still there a bit... got to say it's still better than some other 500's Iv'e driven... but want to carry on and see how good I can get it....
And like I say, if you plug the feed hose off, it appears to improve things (or may be it cooled down and is fueling a bit richer now??) who knows, just messing really.
May have another go with MA at some point... cheers