Bypass Stepper?

[Chown]

Hi all,

I know there's lots of threads on here about stepper troubles, but recently I've read threads about bypassing said stepper. My mate has bypassed his on his Elise and i've read that it is possible on TVR Rover V8's.

I achieved this by blocking the rubber pipe (using a water pipe stopper)between the plenum and stepper and refitting the pipe.

Problem is it only just about idles and makes a hell of a lot of noise eminating from the port where the idle screw is sited. I had to wind the idle screw right out and still i only achieved 800rpm max.

The noise is definititely coming from the idle screw port within the plenum inlet. I'm guessing that a lot more air is flowing through here to maintain idle without the stepper?

Problem is the noise doesn't go away once the revs are lifted?! I'd have thought that when driving with some throttle open the in-coming air would take the path of least resistance (through the butterfly) and not try to flow through the idle port?

My car ('96 5 litre) has a Tornado chip and was mapped by Mark Adams, but i can't imagine this effects the idle settings.

Am i messing unduly or have a stumbled across something weird?

Thanks.

[LordGrover]

I'm no expert, but I understood that to bypass it you get the engine up to running temperature then unplug it. It'll then be set for normal running.
I'm sure someone'll be along to correct me soon.

[shpub]

Why bypass the stepper? It does a pretty good job of controlling the idle.

If you want to bypass it then disconnect it when warm but also be aware that the ECU will report this as a fault code and may switch to one of its limp home modes.
If it ain't broke, don't fix it.

[Chown]

Yeah i'm with you on the "If it ain't broke thing", but my 5 litre suffers from this awful engine overrun rattle (that nobody seems to be able to truely identify) at about 1200rpm, and the stepper controlled idle sits at 1200 for a while making it quite a nuisance! Without the stepper the idle drops thru 1200rpm quickly and the noise is far less perceptable. That is the only reason for trying it!

[richb]

I believe it is perfectly normal for the steppa-motor to pause on occasions at 1,100/1,200 revs momentarily before settling back to 800/900. . Rich...

[david beer]

Chown said:

Yeah i'm with you on the "If it ain't broke thing", but my 5 litre suffers from this awful engine overrun rattle (that nobody seems to be able to truely identify) at about 1200rpm, and the stepper controlled idle sits at 1200 for a while making it quite a nuisance! Without the stepper the idle drops thru 1200rpm quickly and the noise is far less perceptable. That is the only reason for trying it!

Isnt it something with camshaft and lack of thrust washers or something. Mine did it and i hated it, in fact was half the reason for the engine work. If it is that noise,then all dealers indies know about it, i was always told to forget it, but i could not.

[GreenV8S]

I don't have a stepper motor on mine, just block it off and wind the base idle out, if you run out of travel then wind the throttle stop out a little too - you should reset the throttle pot if you do this. I sympathise with the ain't broke / don't fix school of thought but on the other hand it causes so much grief when it goes wrong for relatively little benefit that I have no qualms getting shot of the thing.

[David H]

My car drives better without the stepper motor. The shunting at low speed was reduced and the way the engine speed returns to idle when I wanted it to rather than when the stepper wants.

[Chown]

Re GreenV8S comment..... I don't think there is an adjustable throttle stop on mine. From memory I think it just stops against a steel ball. I suppose its possible to drill and tap and fit a sprung adjuster from another car, but I'm really into messing territory now!

Does yours make the huge sucking noise caused by the abrupt idle port opening in the plenum inlet? Or as i guess just lifting the butterfly off its base is enough to stop this?