Evening Gents..

An unusual issue that has plagued my P38 since i bought it is an iffy cold start.

If you fire her up the revs will bounce between what seems like 250 and 1000rpm, it'll do this a few times before settling down to a good idle. if you give her some throttle it sorts itself out faster.,

However I learnt that if you give her a TINY bit of throttle when starting it stops the hunting but will settle to a very low idle..

Once it's HOT she purrs like a V8 Kitten and sits at the correct idle speed.

I should note there are no misfires..

Cheers gents.

Clean the idle air valve.

Right it has started to Die when i start it from cold..

It is running on all 8 very well the idle is just all over the shop..

It is idling at 100rpm..

When it starts to warm up the idle raises to 450rpm.

Looks like it has failed completely..

Oh well..

H

Did you clean/do anything with the idle air valve? If so, the other possible cause may be a vacuum leak, specifically I'd have a look at the crankcase breather that goes from the rocker cover to the inlet manifold. Having done the valley gasket on the Disco this week, I discovered that pipe is well past its best on mine (split at the end). Didn't have a replacement at the time so moved the clip around for now to cover the split up, I have some vacuum hose arrived today to hopefully replace it (if I can get it to bend in an acceptable manner without kinking)

Equally check any other vacuum lines as well while your there (including the one for your lpg vapouriser even though the lpg isn't working) Sometimes they can come into contact with other things and rub holes in the vacuum line where it gets plugged some of the time and not others.

More than likely diaphragm in LPG vapourisor damaged

Only if he's running it on LPG. If you are Henry, switch back to petrol 30 seconds or so before switching off. That will allow any leaking gas to be used up so it won't flood the inlet. If only running on petrol, it isn't that as the solenoids won't have allowed any gas into the reducer.

Thanks Brian the breather in the rocker cover was loose, i've put it back on with a new clip..

I haven't restarted it yet!!

Symes it does it on Petrol and Gas

Richard..

She's running on both petrol/Gas she starts on petrol and the idle drops to 100 and it then cuts out, it is running on all 8 with no missfires..
When she starts to warm up the idle raises up to 450rpm on Gas and Petrol she runs great on both but the idle is crazy low..

H

Next time you run it, switch over to petrol a minute or so before turning it off. If it still does it, then it isn't a leaking diaphragm.

Is your RPM indication okay? I have a bit of a hard time believing it will actually continue to run at 100 RPM.

On my omega V6 LPG every so often I had to spray carb cleaner through gas lines due to LPG gung build up that effected idle

One thing of note "not at all related" is even at 150rpm the oil pressure light stays off no flickering!!

And yes before anyone says it, the light does work!!

Did you check the IACV? The Thor one is different to the GEMS one - GEMS has a stepper motor that gets gunked up, but the Thor is a different setup where it's a couple of electromagnets which depending on the current being pulsed through them will hold a spring loaded air valve in the correct position.

I've had it on mine where it's got really gunked in there and the valve part hasn't been able to move freely.

A question for the knowledgeable out there on the IACV, 98MY GEMS 4.6. I note that mine sits at LTAI of 255 and STAI of 250, with the STAI very occasionally dropping to single digits whilst on the road (from looking a a nano recording file). The IACV position seems to sit somewhere between 20 and 36 at any given time.

The engine idles sweetly and is always spot on for RPM at idle. I note that the plug over the air adjustment screw is out, so I wonder if a PO has tweaked this for some reason and the system is compensating, or are these the sort of numbers you would expect to see?

Don't understand? Are you talking about long and short term fuel trims (LTFT and STFT)? 20 to 36 on the IACV is correct at idle but it should go up under acceleration as it opens up to give a cleaner pick up as you open the throttle.

Martyuk wrote:

Did you check the IACV? The Thor one is different to the GEMS one - GEMS has a stepper motor that gets gunked up, but the Thor is a different setup where it's a couple of electromagnets which depending on the current being pulsed through them will hold a spring loaded air valve in the correct position.

I've had it on mine where it's got really gunked in there and the valve part hasn't been able to move freely.

I noticed today the throttle cable was looser than a loose thing and the throttle seems to be sealed tighter than a nats arse..

I gave the throttle a few good prods and voila' problem solved!!

Odd car this one..

I noticed the idle was getting a bit odd after giving it a bit of pedal to the metal going past some cyclists..

From what i understand you just take air pipes off the IACV and spray some cleaner int here?

Or does the entire unit come apart?

Gilbertd wrote:

Don't understand? Are you talking about long and short term fuel trims (LTFT and STFT)? 20 to 36 on the IACV is correct at idle but it should go up under acceleration as it opens up to give a cleaner pick up as you open the throttle.

No, the Long Term Adaptive Idle and Short Term Adaptive Idle.

Air adaptive idles - I spent a while playing with mine after I cleaned the old stepper motor and airways. It seems that there is a balance between high figures on long and short term vs (better?) lower figures and the IACV % adjustment. 'Perfect' (say 21) % IACV, warm, all extra kit turned off on mine raises the adaptive figures, up on IACV nearer the 30% and they fall again. However, the actual behaviour of the stepper at light throttle and the % seem to be more important than the figures for the two (short and long-term) adaptives, which also change readily. It's probably important in some way, but it seems to be more noticable to the running to get the Idle % in the right range, or close to it. My car has always driven better with a slightly high IACV % tbh, it's probably due in my case to worn out parts. As the adaptives adjust for various factors including aged components, I'm currently ignoring those rightly or wrongly. It's the fuel trims and actual adaptive airflow that seem to throw a spanner in the day to day running if they go off. I had a sketched out MAF sensor at one point and that kept maxing out the a/f trims. Haven't seen idle trims hit a stop point, but they do seem to move around a lot anyway.

From the Nanocom GEMS manual:

Short term idle (steps): This is the value that the GEMS use’s to regulate the current idle speed
to take into account current engine load, temperature etc. It can be manually altered here may
later be changed by GEMS. The value is in steps and it can be a number between 0 and 255.

Long term idle: This is the value that the GEMS learns over a period of time to take into account
manufacturers tolerances on components which affect overall idle speed. This value cannot be
modified, but it can be reset, forcing the GEMS to re-learn this value.

So don't worry about it. If you reset the adaptive values it will reset but will then learn and set itself where it needs to be.

All good then, many thanks.

Right another issue!!

From cold start her idle is 1700rpm when she starts to warm up the idle jumps from 1700-1000 and then settles at 1100..

One up to temp it drops rapidly to 850 and she idles fine..

All day fine..

But once cold it is going insane!!

I'm torn between IACV and TPS..

I noticed it only started to happen after a i gave it full throttle, "which i've never done" lol