Help! Stalling on return to idle

[Chris71]

I had an awesome winter blast in my Chim yesterday - really started to gel with it - but a couple of times when, for example, I came back to traffic lights and stuck it in neutral it stalled.

Each time was when the car was stationary with my foot off the gas. It only happened intermittently during the drive and I was always able to re-start immediately afterwards without issue. Any idea what it might be?

[darkcat]

hmm, one of those "could be anything" ones...

- idle stepper
- throttle potentiometer
- AFM
- vacuum advance
- fuel pressure regulator
etc etc...

try cleaning the idle stepper first..

[Chris71]

Just did a search and the symptoms seem to match people who've had stepper motor issues. What I can't see is any advice on how to clean it. Anybody got a link?

The cut out hasn't happened before (although admittedly I haven't had a chance to drive the car a lot in the two months or so I've had it...) but it's always been conspicuously thirsty, so there may be more to it than the stepper motor. Does sound like a good start, though.

[miniman]

There's a decent write-up here:

http://www.tvrsseries.com/steppermotor/steppermoto...

One thing worth trying is to get the engine warm and idling at a steady speed, then disconnect the stepper (with the engine running). My old Chim refused to idle properly but when I did this, taking the stepp out of the loop, it was perfect. Quite rough when cold, but fine after a few minutes running. Certainly helps narrow down the cause.

[Chris71]

Thanks, will give it a go.

ETA Is it really necessary to use a fresh washer every time you remove the stepper motor?

Edited by Chris71 on Sunday 16th January 13:13

[anonymous-user]

Just to add, I had these symptoms three weeks ago and a new coil and ignition amp, with some tidy up wiring has transformed the car, and the idle , that is now perfect.

[miniman]

cliffords said:

Just to add, I had these symptoms three weeks ago and a new coil and ignition amp, with some tidy up wiring has transformed the car, and the idle , that is now perfect.

Interesting - I've got some misfire problems at the moment and amp / coil are next on my list. Where did you buy yours from?

[Chris71]

I haven't had a chance to take it for a run yet, but I did remove the stepper motor. I'm not convinced that's going to turn out to be the problem, though, because it looked pretty clean (I think it's been cleaned relatively recently as I was able to losen it by hand...)

This is as it was removed:


And after a clean up:


What exactly does the stepper motor control anyway - is it EGR?

ETA: Continuing to get rather high fuel consumption - particularly when driven gently (low revs, light load) - but the engine feels good when you're on a run. Does that suggest the air flow sensor and lambda sensors (I presume there's one for each bank?) are the next suspects if this doesn't work?

Edited by Chris71 on Sunday 23 January 12:09

[dog man]

Set base idle?? Mine has never stalled for me but when the TVR center recently did some other work they reckoned it did for them (still find that weird) anyhow they adjusted/set the base idle when I thought it was spot on/okay.

[blitzracing]

The stepper looks OK. Before you get to complex whip a plug or two out (on opposite sides of the V8) and have a look at the colour. Each side of the V8 has independent fueling, so it will tell you a lot. Black means to rich which is likely of the fuel consumption is high, and common faults this would be an AFM fault or possible misfire. If you have a test meter, plug it across the black and white wires from the Lambda probes, and check they are switching between 0 and 1 to 1.2 volts at idle at about .5 second intervals with a warm engine. If its stuck at 1 volt or more you have a rich mixture, or 0 volts over lean. Diagnosis is much better than guesswork.

[dog man]

Excellent advise there^^

[Chris71]

blitzracing said:

The stepper looks OK. Before you get to complex whip a plug or two out (on opposite sides of the V8) and have a look at the colour.

I actually tried to do that this morning when I did the stepper motor, but - and I'm rather ashamed to admit this - I couldn't see how to get the spark plugs out! I'm assuming they're all like this, but there's some sort of extension on the top of my plugs which means you can't get a socket straight on there.

Never thought I'd have to ask this, but: How do you get the spark plugs out?

[dog man]

Those extensions pull off too. Mine were tight to get off. Careful with the plugs when re fitting, very easy to cross thread

[Chimpafrolic]

Chris71 said:

I had an awesome winter blast in my Chim yesterday - really started to gel with it - but a couple of times when, for example, I came back to traffic lights and stuck it in neutral it stalled.

Each time was when the car was stationary with my foot off the gas. It only happened intermittently during the drive and I was always able to re-start immediately afterwards without issue. Any idea what it might be?

Chris before you get completely fixated with the stepper motor I have a question.

"Is your car cutting out when you came to a junction after slowing fairly rapidly from speed?"

IE lift off throttle, brake, come to a stop and then it cuts out?

If these are your symptoms its unlikely to be the stepper motor, its far more likely to be the road speed signal to the ECU.

As I understand it in a Range Rover the speedo delivered this signal, in a TVR the speedo is different and needs a little box of electronics to supply the same low speed signal to the ECU.

The idea is in most throttle lift off conditions it is preferable to kill the fuel, but at low speeds this would result in the engine cutting out at junctions.

So below 3mph on throttle lift off a special signal is sent by the little box of electronics & read by the ECU to reinstate fuel and keep the engine from cutting out.

The signal isn't very strong even when things are working perfectly so any corrosion on the contacts is enough for the signal to be lost resulting in junction stalls.

My car did this, I eventually tracked it down to a bad connection on the wire at the back of the speedo that sends the primary signal to the little box of electronics.

All the little box of electronics does is convert the speedo signal into something the ECU can read & recognise.

Any way, once the connections were made good the fault completely disappeared.

I can now come up to a junction slowing from speed in a throttle lift off condition and the car holds the correct idle & doesn't cut out.

If any of this sounds like your fault just remove the wires from the back of the speedo and reconnect them, this was enough in my case to get everything working correctly again.

[Mr MoJo]

Chimpafrolic said:

Chris71 said:

I had an awesome winter blast in my Chim yesterday - really started to gel with it - but a couple of times when, for example, I came back to traffic lights and stuck it in neutral it stalled.

Each time was when the car was stationary with my foot off the gas. It only happened intermittently during the drive and I was always able to re-start immediately afterwards without issue. Any idea what it might be?

Chris before you get completely fixated with the stepper motor I have a question.

"Is your car cutting out when you came to a junction after slowing fairly rapidly from speed?"

IE lift off throttle, brake, come to a stop and then it cuts out?

If these are your symptoms its unlikely to be the stepper motor, its far more likely to be the road speed signal to the ECU.

As I understand it in a Range Rover the speedo delivered this signal, in a TVR the speedo is different and needs a little box of electronics to supply the same low speed signal to the ECU.

The idea is in most throttle lift off conditions it is preferable to kill the fuel, but at low speeds this would result in the engine cutting out at junctions.

So below 3mph on throttle lift off a special signal is sent by the little box of electronics & read by the ECU to reinstate fuel and keep the engine from cutting out.

The signal isn't very strong even when things are working perfectly so any corrosion on the contacts is enough for the signal to be lost resulting in junction stalls.

My car did this, I eventually tracked it down to a bad connection on the wire at the back of the speedo that sends the primary signal to the little box of electronics.

All the little box of electronics does is convert the speedo signal into something the ECU can read & recognise.

Any way, once the connections were made good the fault completely disappeared.

I can now come up to a junction slowing from speed in a throttle lift off condition and the car holds the correct idle & doesn't cut out.

If any of this sounds like your fault just remove the wires from the back of the speedo and reconnect them, this was enough in my case to get everything working correctly again.

This is exactly what mine started doing last week when out on a TVRCC run. In the end I was tending to slow down to junctions much earlier than usual to keep the revs up and prevent it cutting out.
Not sure if it was my imagination but it seemed to do it more when coming to an abrupt halt on a downhill slope.
I had pressumed stepper motor or maybe immobiliser problem as at one point it wouldnt restart until I blipped the key fob on and off.
I'll also check the above suggestion this week aswell now and keep an eye on this thread

[Chimpafrolic]

Mr MoJo what you are describing is the classic road speed signal fault.

You are correct the fault is much worse on rapid deceleration & braking so its no surprise this would be worse when coming down a hill to a junction.

I could avoid cutting out if I went down through the gears and reduced my speed slower.

For a while I also took to knocking the car into neutral and left foot braking while using my right foot on the accelerator to keep the revs up, thus avoiding cutting out.

But it was all a bit of a dance and rather dangerous in town too, often I would simply forget my dance steps and the fault became more & more annoying.

Its well worth checking those connectors, removing & reconnecting them completely solved the problem for me.

[dog man]

Interesting about the Range Rover/TVR ecu/speedo relationship. I heard they fitted this gizmo because RR's were speed limited so in order to use the RR ecu, this device makes the ecu 'think' the car is doing half the speed (or 30% less?, I don't know exactly)

The same person said this thing was often to blame for shunting ??

[Chris71]

Chimpafrolic said:

Chris71 said:

I had an awesome winter blast in my Chim yesterday - really started to gel with it - but a couple of times when, for example, I came back to traffic lights and stuck it in neutral it stalled.

Each time was when the car was stationary with my foot off the gas. It only happened intermittently during the drive and I was always able to re-start immediately afterwards without issue. Any idea what it might be?

Chris before you get completely fixated with the stepper motor I have a question.

"Is your car cutting out when you came to a junction after slowing fairly rapidly from speed?"

IE lift off throttle, brake, come to a stop and then it cuts out?

If these are your symptoms its unlikely to be the stepper motor, its far more likely to be the road speed signal to the ECU.

Interesting... That does describe it pretty much perfectly.

I'm still curious to check the plugs and the AFM signal though - I've just done my second (relatively scientifically recorded) MPG calculation and it's climbed to a dizzying 15.1mpg.

Although I am bearing your comment about running temperatures in mind too - it eventually seems to settle in the lower middle part of the gauge, but it does take quite a while to warm up.

[Chimpafrolic]

Chris71 said:

Chimpafrolic said:

Chris71 said:

I had an awesome winter blast in my Chim yesterday - really started to gel with it - but a couple of times when, for example, I came back to traffic lights and stuck it in neutral it stalled.

Each time was when the car was stationary with my foot off the gas. It only happened intermittently during the drive and I was always able to re-start immediately afterwards without issue. Any idea what it might be?

Chris before you get completely fixated with the stepper motor I have a question.

"Is your car cutting out when you came to a junction after slowing fairly rapidly from speed?"

IE lift off throttle, brake, come to a stop and then it cuts out?

If these are your symptoms its unlikely to be the stepper motor, its far more likely to be the road speed signal to the ECU.

Interesting... That does describe it pretty much perfectly.

I'm still curious to check the plugs and the AFM signal though - I've just done my second (relatively scientifically recorded) MPG calculation and it's climbed to a dizzying 15.1mpg.

Although I am bearing your comment about running temperatures in mind too - it eventually seems to settle in the lower middle part of the gauge, but it does take quite a while to warm up.

Chris 15mpg (even for a 5 litre car) indicates you either have a very heavy right foot or your car is asking you for a service.

If it were me I would start with these three basic and inexpensive things:

1) Check & adjust your ignition timing

2) Remove the nasty old foam air filter and give it a damn good clean (or better still fit a new K&N one)

3) Block off the lower half of your rad (or more) to bring the running temperature between 80 - 90 degrees

There are lots of other good practice things you can do with a RV8 to help it run sweetly, changing your plugs, plug leads, distributor cap, rotor arm (genuine Lucas only) & making sure your vac advance module is working correctly are just a few examples.

But I wouldn't mind having a bet with you that just doing the three things I have listed above and your car will jump from 15mpg to just over 20mpg driving it exactly the same way.

NB: To set your ignition timing correctly you really need a decent strobe that you can set the advance and see the RPM.

Here are the settings (Vac advance disconnected)

• 8 degrees of advance at an 800rpm idle (advance commences at 1000 rpm to show 10 degrees)
• 28 degrees of advance at 4,000rpm

A defective vacuum advance module is also not uncommon and will have a noticeable negative effect on economy as its essentially an economy device designed to give you a bit more advance on light throttle cruising.

To test it take the distributor cap off, remove the rotor arm and plastic base cover, suck on the vac advance pipe and see if the base plate moves.

Often the diaphragm is split inside the vac advance module so it wont hold vacuum, sometimes the mechanism is seized, either way you need to replace it to get your economy back.

My Chim came with a fully stamped up service book and when I collected it she had just been serviced by a well known TVR specialist.

Because I know how tempting it is for a commercial enterprise to skip basic service tasks I decided to give the car a really thorough no expense spared service myself.

Amongst other things I found.

• Air filter completely clogged

• Air filter rubber collar split

• No 7 plug lead shorting on the exhaust manifold and all the others looking very sorry for themselves

• Rear brake calipers partial seized causing binding

After my belt and braces service my car went from 18mpg to 27mpg on a run.

You are very welcome to pop over to me in Watford if you want a few hands on pointers and the loan of a decent advance strobe with tacho.

Or why not join Frenchie & I for a service session here:

http://www.pitstartgarage.com/

[miniman]

Great tips, thanks! I will be checking some of these ASAP.