Idle Flare at Cold start

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Idle Flare at Cold start

Postby peteoddcar » Wed 19.06.2019, 13:02

Hi
Probably one for Geoff ?
Not sure if there’s anything amiss - but when I start the car when cold the revs immediately go up to about 1500/1800.
I don’t think it’s that healthy to ramp up that quickly before the oil has got under pressure.
When it’s been parked for a month or more I normally crank it with the inertia switch off so I can get the oil circulation under way.
It’s an early pre catalyst car with no cal or engine mods.
Idle valve not resetting maybe?
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Re: Idle Flare at Cold start

Postby HJ2 » Wed 19.06.2019, 16:04

My bet would be a leak in the intake manifold...
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Re: Idle Flare at Cold start

Postby Giniw » Wed 19.06.2019, 16:43

The IAC has a correction multiplier so I am not so sure about that? It would compensate the leak?
Plus, why would it be only when starting the engine?

peteoddcar > you may try to put the ignition on and off a few times before you start as it resets the IAC each time so if it's a bit seized when cold and the car has not been used for a few days it may free it before crank the engine.
Of course that won't cure anything but it might be a confirmation your IAC is a bit seized?

I think the idle speed is raised when the temperature is very low, so maybe you could check your coolant temperature sensor, too? (or another temperature sensor, I can't remember if there are other ones)
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Re: Idle Flare at Cold start

Postby Simon_P » Wed 19.06.2019, 18:11

HJ2 wrote:My bet would be a leak in the intake manifold...

+1
How quickly does it settle down to normal idle?
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Re: Idle Flare at Cold start

Postby peteoddcar » Wed 19.06.2019, 19:44

About 2 -3 seconds - then drops to a normal cold fast idle
I’ll try try the key on off - I dont think it’s an air leak but not really checked to be honest.
It is always fine after that initial start some times I key it straight off as it fires up then on the re crank its fine sometimes stumbles a bit but settles to about 1000/1200 never flares again.
I’ll take a look at the idle valve tomorrow. Good call thanks
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Re: Idle Flare at Cold start

Postby Simon_P » Wed 19.06.2019, 20:23

Yes sounds like an air leak as it takes a couple of second for the IAC to compensate for it. You can check by putting it into service mode and checking the idle. Instructions in the wiki.

The IAC appears to be working as the revs are reducing.
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Re: Idle Flare at Cold start

Postby Simon_P » Wed 19.06.2019, 20:28

Giniw wrote:The IAC has a correction multiplier so I am not so sure about that? It would compensate the leak?
At startup it is expecting to be at a certain point depending on conditions . Yes it would compensate for a leak unless it was too big which would mean that the revs were high once the engine was warm.
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Re: Idle Flare at Cold start

Postby John_W » Wed 19.06.2019, 21:04

Sounds like an air leak to me and my “usual suspects” would be all the nipples and right-angle connectors at the back of the plenum. And even if they are all connected, check that something is connected to them
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Re: Idle Flare at Cold start

Postby peteoddcar » Fri 21.06.2019, 14:32

Just had a good look nothing appears not connected no splits
I tried the key on and off a few times made no difference but I think I can hear the IAC working.
Engine running I can’t hear any whistles or hissing
I sprayed some brake cleaner around the intake plenum, injectors, throttle body etc. No change in engine note or anything to suggest it’s having a whiff of the vapour.
I also checked the box with six screws on top (spark arrester? ) all clean gasket looks good.
There’s an adjusting screw under a cap on the TB haven’t touched it - what’s it for ? air regulation fast idle ?
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Re: Idle Flare at Cold start

Postby alan e » Fri 21.06.2019, 14:55

Just a maybe do you have air con and if so is it switched off.
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Re: Idle Flare at Cold start

Postby peteoddcar » Fri 21.06.2019, 17:23

Thanks Alan, good call but no air con on my car.
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Re: Idle Flare at Cold start

Postby GeoffSmith » Fri 21.06.2019, 18:17

My leak (which gave similar symptoms) was the pipe from the dreaded right angle connector on the plenum to the reservoir in the nearside wing. Replaced by silicone (with no right angle) and all sorted. Rather than pulling the wheelarch liner off, I diagnosed it by plugging the hole in the plenum… then when it was confirmed pulled the wheelarch liner off.
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Re: Idle Flare at Cold start

Postby peteoddcar » Fri 21.06.2019, 19:35

Geoff thanks
I’ll check in the morning - I’ll look for a pipe which goes to the inner wing area can you recall where it exits the manifold?
Is it a 6-8mm or 3mm ID pipe?
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Re: Idle Flare at Cold start

Postby Simon_P » Sat 22.06.2019, 11:33

I noticed that the Green car when I started it a couple of days ago was initially at about 1800 rpm I can't be sure as I wasn't looking specifically at that. But it had stood for a week. In about 1/2 a second the revs were normal. What I did notice was the tappet clatter for about the first second, which I was listening out for. I have recently put in a new Mann filter and my first thought is that it doesn't have an anti-drain valve so there is insufficient oil at start-up. I mention this as your concern is partly about there not being oil circulation.

I'm yet to check the spec of the filters, so its still a theory.

The blue car has been stood for a couple of days so I will start that later and make note of the revs. (it now also has a Mann filter and rattles on startup hence my investigation).

Just to add. I have recently checked both for vacuum leaks and set the idle.
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Re: Idle Flare at Cold start

Postby peteoddcar » Sun 23.06.2019, 10:15

I just started mine with the under wing pipe clamped close to the manifold, exactly the same ( and as you describe)
The rattle is also how you describe it, I have had a K&N filters for the last two oil changes ( it’s due another but can’t do it at present ).
I have just had the cam belt, pump and idlers done, my mate did the job whilst I watched and the belt that came off was very slack and starting to loose rubber particles, since having the belt done the engine is really a lot more responsive.
But the idle flare has got more noticeable.

So I am now wondering if I should get back and re check the CAS and base ignition timing as this I know was set about two years ago when I fitted a new sensor to it, with the loose / stretched belt

Oddly having said all that there was no rattle at all this morning.
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Re: Idle Flare at Cold start

Postby Simon_P » Sun 23.06.2019, 14:14

peteoddcar wrote:Oddly having said all that there was no rattle at all this morning.
I started the Blue car yesterday evening - 1200 rpm no rattle.

I have checked a proper old stock Lotus filter and it has an anti drain valve. I also checked a Mann Filter (W811/80) and it too has an anti drain valve.

Checking base timing and idle is always a good place to start.
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Re: Idle Flare at Cold start

Postby peteoddcar » Sun 23.06.2019, 16:18

Base timing and idle set tomorrow
I’ll post the result.
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Re: Idle Flare at Cold start

Postby Giniw » Mon 24.06.2019, 13:07

As for the rattle, couldn't it be just the hydraulic tappets?

As for the MANN filters, I think they do have an anti-drain valve, don't they?
https://www.mann-filter.com/mann-filter ... ews%5D=397
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Re: Idle Flare at Cold start

Postby peteoddcar » Mon 24.06.2019, 16:05

Well it pays to go back to check the basics ! I should know better than to jump in half cocked !
Diagnostic mode procedures followed to the letter, except I have a timing light with an advance controller so I reference to the TDC mark which is easier and can be seen without taking front wheel off.
Paper clip in place
Base ignition was out by about 4 - 6 degrees retarded corrected.
This put the idle up to about 1200 followed procedures in Wiki dropped back to 950 on the air screw,
Switch off out of diagnostic
On warm start it goes to 11/1200 then drops to 950 solid after no more than a second. Left it for 5 hours about 20c ambient
Started exactly the same.
I’ll try it again in the morning but I think it’s fixed
Thanks for all your inputs.
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Re: Idle Flare at Cold start

Postby peteoddcar » Tue 25.06.2019, 19:24

Started from cold 20c ambient 12/1300 for about a second or two then settled back
No rattles either
I am happy
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