RV8 idle control stepper

[nigelj77]

Hi folks,

I've had my griffith 500 3 years now and occasionally it likes to hold onto revs at idle, typically around 1200rpm rather than the 900 - 1000 normal.

I believe supplying dealer changed the stepper when I complained about idle speed.

Do they typically only last a few years as mine seems worse at the moment, took it out and cleaned it, seemed great yesterday then not great again today?

Thanks in advance, Nigel

[phillpot]

I believe you pay your money and take your chance with a cheap one or pay more for a supposedly quality one.

The cynical me says seller doing foc rectification would choose the cheaper one

[steviegtr]

Been down this road. I did a youtube video about it. But essentially i removed the new one fitted by a tvr specialist Zinc in colour. I then purchased a genuine one (Black) & fitted this. Problem sorted. The Zinc one was charged to the last owner £75. I assume that included his profit margin. The one I bought was I think £120 so you can see why some buy the cheap one. Link for anyone wanting to watch. https://youtu.be/-xPZfSgAqm8
Steve.

[GreenV8S]

They're notorious for getting gummed up and you need to check that the whole of the air bleed circuit and butterfly are clean, not just the stepper motor itself. But if it's behaving inconsistently and you believe it's mechanically OK then you need to find out whether the problem is the stepper motor not responding correctly to the signals the ECU sends it, or the ECU getting a duff input causing it to raise the idle. Either a missing road speed signal or faulty coolant temp signal can cause idle speed glitches.

[BritishTvr450]

I think like most of the electrical components in the ignition/fuelling system heat effects old or poor quality components.
In the case of the age old stepper motor issue this must be considered as a big part of the problem still!

One easy diagnostic trick is to turn engine off when erratic idle appears. If for a short period after you re start the engine the idle remains stable then either blipping the throttle or after a drive the raised or erratic idle returns this can be a sign the stepper motor plunger is sticking and not moving in line with the electrical pulses the system has provided.
This causes the stepper to be out of sinc with the Ecu reading of its position.
The system understands it’s position via those individual pulses so if it sticks momentarily the Ecu gets confused and coupled with the lambda readings try’s to constantly adjust fuel/air settings.
The issue is simply the stepper is out of position.
Turning off ignition returns the stepper to its set position. This is often why the car will now run ok again until age/crud/heat causes the stepper to stick and the symptoms return.

In view of its importance a cheap one has to be out of the question ( as a long term fix) but even the expensive ones have been called into question by some.

As others often call out, induction leaks will also play havoc with the system so these need to be discounted before you can be sure but if the problem is intermittent and often when cooled down car runs ok ok for a period this could be a symptom of stepper sticking issues.
It’s also correct to say a fouled water sensor will have a similar effect in causing usually rough/ rich running but you would expect that failure to be constant and not erratic.
The erratic bit is why the o/p is right in looking at stepper issues.

If a replacement works for a year or two you have to consider that normal!
If any fail whenever it’s hot it’s useless.
This is the same issue with AFM
The more you read into the system the more you see similar symptoms can be caused by a number of reasons.
Prudent move is to simply use RoverGauge to read what’s going on and narrow down the possibilities.

I’d advise anyone to buy RG and take notes of readings when the cars running well so you have a comparison table before things have gone tits up.

All this comes about through poor product manufacturer so you have little choice but buy what you hope will be the best and keep your fingers crossed it works when hot.
Ironically the stepper housing and plenum run quite cold when travelling at speed so it’s slow moving traffic/ running the car stationary that causes heat transfer into stepper area. The stepper goes through many heat cycles maybe in one drive. The Afm is usually constantly red hot.

There’s many an area of a Tvr you can spend money on to improve it and none more so than this area of the car.
In an ideal world we would have a drive in/ out service and your car would be magically transformed with a modern Ecu/ wiring/ sensors and all mapped in a day all for 550 quid but until then we use a few well known guru to do it for us usually over about two weeks for around 2.5-3k which is still money very well spent as it’s not the work of a moment.
Far to expensive in the eyes of a sensible person but by feck if you do do it it’s like going from a carb controlled aeroplane to fly by wire. Reliable crisper and safe.
In the mean time and on 2000 mile a year it’s probably best to just replace steppers every now and then Lol.

[nigelj77]

Thanks for the replies.

I can confirm the stepper is black bodied not zinc coloured, it looks a little different to those I have removed and cleaned and once over replaced in previous TVRs, the "plunger" on the end is silver and once I've seen before are dark grey with what looks like a chemical finish.

The car is due in for a service in a few weeks, I'll hold off replacing and await the opinion of the specialist.

For a car that sees such low miles I can't justify the £2-3K conversion work, it doesn't spoil the fun that much.

[blaze_away]

If you have rovergauge it's easy enough to remove the whole stepper motor then eject the plunger. Clean everything with white spirit then regressed with vaseline. Also clean inside the housing too with cotton buds carefully so as not to leave cotton fragments.

[blitzracing]

You can strip the stepper apart without RiverGauge this way;

Cleaning the Stepper Motor
At its simplest, the motor can be unscrewed from the plenum housing, and all the carbon and oil deposits removed from the head of the metering cone, and some use of carb' cleaner on the keyway may be enough to get the unit working. It’s also worth cleaning out the metering hole inside the plenum. If it still sticks then more drastic measures may be needed. I have now perfected a way of getting these bits to clean, without damage:

Get the car warm

Remove the stepper from the plenum and reconnect it

Block the hole the stepper has come from with something air tight, or even the palm of a hand

Hold the stepper so you can catch the central cone and spring when it comes out

Get someone to start the car. Without the stepper in place it will rev at around 2k- 2.5k (This is noisy!!), but the ECU will try to slow it down by powering the stepper motor and pushing cone outwards. It will do this in a series of pulses, a few seconds apart, until the cone and spring drop out. (assuming they are not completely stuck). It may take a bit of manual help to get the cone to fully release. Now stop the engine and let it cool.

Clean all the muck off the shaft and cone, and lightly lubricate the screw thread inside the motor

To reassemble, wind the shaft back into the motor so far, but align the slot in the shaft with the plastic keyway as best you can by rotating the shaft in its screw thread.

With the engine cool, then reconnect the stepper motor. Power cycle the ignition on and off, (don't start) and the ECU will try to pull the shaft back in each time the ignition is turned OFF. This is the slightly tricky bit, as if the keyway and shaft are not quite aligned it wont pull home, so you may need a few attempts.

[nigelj77]

Thanks for the further information, I don't have a rovergauge and am a little worried about the running engine with stepper removed etc, I'll discuss with the specialist when it's in for service in a few weeks and see what he thinks, I can live with the cost of a new stepper but would hope they had a lifespan of more than 4K miles.

Cheers

Nigel