Cold stalling (not stepper)

[sbirt]

My '98 Griff has developed a problem with maintaining idle when cold. The symptoms are:

Car starts and idles fine. If driven slowly (below 2000 rpm or so) it will still idle ok. If revs rise above ~2000, the engine will die when coming to a stop with the clutch down. It will then re-start and idle fine, only to stall again at the next stop.

This behaviour only seems to happen when the car is not fully warmed up - at a certain point it all starts working fine.

The dealer has lent me a new stepper motor to see if it helps (no) and has replaced the lambda sensor (no change). No faults are reported by the ECU.

I have a sense of impending financial catastrophe (no warranty...) if the trial and error method is continued, and would be immensely grateful for any suggestions!

Thanks in advance,


Simon

[GreenV8S]

Hello Simon!

I would suspect a combination of a faulty speed sensor and / or base idle speed set too low.

[beano500]

I've read your symptoms through twice, sbirt, but can't think it is likely to be anything particularly £££. A number of possibilities spring to mind and I'd back Peter's thoughts...

But the dealer (if worth his salt) should be able to take it on and work it out, I'd have thought - It's not rocket science after all*


*Rocket science is only shoving hydrogen and oxygen in a box with a hole in one side, anyway!

[simon.b]

Sounds like a air leak at the brake servo or on the feed. I haven’t checked how this actually works on a Griff, but the air is usually taken from the inlet manifold.

Cheers,

Simon.

[jigs]

How do you set base idle speed?

[sbirt]

GreenV8S said: I would suspect a combination of a faulty speed sensor and / or base idle speed set too low.

When it doesn't actually die, the idle seems to always be at 1000 rpm or just over, which I think is about right (but am willing to be corrected). If the speed sensor is responsible, would you expect the engine to stall if the clutch is depressed while still travelling at speed? I shall have to go out and try this.

[donatien]

jigs said: How do you set base idle speed?

I thought idle was set by the stepper motor, though there is also a grub screw on the plenum. I don't believe it's used to alter idle since the older Wedge engines.

I sometimes have an issue if I start up again after the engine is warm. The idle can creep down to 500-600. Whilst the engine doesn't stall it does run a shade lumpy. Very occasionally when this happens I can hear what I think is the stepper then "hunting" out the revs and fluctuating between 500 and around 1100.

On these occasions a quick stop and restart seems to put it back to around 900-1000 revs as per normal.

[shpub]

Covered in detail in the bible. Yes the stepper sets the idle but the grub screw is used to set up what is called the base idle i.e. the idle rate without the stepper. This in practice should not be touched once it has been set but it does get touched.

The speed controller works off the transmission independent of the clutch so dipping it will not simulate the slowing down process.
This could also be a faulty temp sensor or a combination of all three. The speedo sensor problem should create a fault code.

Steve
www.tvrbooks.co.uk

[jigs]

Shpub - are you saying that the grub screw on the plenum sets the base idle speed on a 4.3 precast Griffith?

[shpub]

jigs said: Shpub - are you saying that the grub screw on the plenum sets the base idle speed on a 4.3 precast Griffith?

Yes. On non stepper engines, it was used to set the idle on its own. A lot of people then thought that was still the case with the stepper motor cars and twiddled with it. Unfortunately the steeper comes in and starts to play expecting a base level idle set by the grub screw. As I said, should be set and then left alone but often is played with. As a result it might need resetting. Pages 103 to 106 in the bible. Clean the stepper and throttle butterfly. Squash the air bypass hose and then adjust grub screw for 400-500 rpm.


>> Edited by shpub on Friday 30th May 09:52

>> Edited by shpub on Friday 30th May 10:00

[jigs]

Thanks Shpub. What effect does the adjustment on the hot wire air flow meter have on idle speed, if any?

[shpub]

jigs said: Thanks Shpub. What effect does the adjustment on the hot wire air flow meter have on idle speed, if any?

Nothing it is used to calibrate the meter. Touch this and the ECU settings get screwed up. Basically leave well alone.

[cess]

Mine had exactly the same symptoms - I found the metal grid in the mouth of the airflow meter was almost blocked and the air filter was also near as dammit blocked.
At least it doesn't cost anything to check them!