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Gtir Motorsport club » Tech room » Help and Advice » Intermittent erratic idle

Intermittent erratic idle

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1 Intermittent erratic idle on 21st September 2017, 6:48 pm

Cosmic73

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So I've had 2 trouble free years since I rebuilt the engine and done more than 30k miles without a hitch, So i suppose my luck had to run out eventually and i hope it's nothing serious.
Noticed on my 30 minutes commute home a little hesitation as accelerated and idle hovering slightly, but as got nearer home it got worse where it was almost stalling at idle.
Took a video below and when I stop feathering the accelerator it gets really bad with black smoke coming out the exhaust and around the engine.
https://youtu.be/CeQZUtVTThU
Fault code reads 5 long, 5 short so all ok there.

An hour later I tried the engine again and the same problem occurred. Tried it again 1 min later and all ok ish.
I thought I'd check the following;
Spark plugs and spark,
Loose wires,
Timing,
I'd there anything I should consider?

2 Re: Intermittent erratic idle on 21st September 2017, 7:22 pm

mike74

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Air leak! Try the usual culprits like boost and vacuum pipes and the bov leaking. If theyre ok maybe the ignition module overheating? Does the idle improve or worsen if you unplug the maf? Theres a sticky on here about its resistance so thats a quick easy check.
Is the standard pcv valve to the left rear of the head still there? That's another potential problem if its fubar

3 Re: Intermittent erratic idle on 21st September 2017, 7:24 pm

johnny gtir

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moderator
moderator
Black smoke is un burnt fuel mate why it's also around the engine I don't know. What's the rattle or is that something none related. Boost pipes ok ? As would explain idle and black smoke

4 Re: Intermittent erratic idle on 21st September 2017, 7:25 pm

mike74

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Also, has your vacuum at idle changed since this started?

5 Re: Intermittent erratic idle on 21st September 2017, 7:25 pm

johnny gtir

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moderator
moderator
What's the turbo like ?

6 Re: Intermittent erratic idle on 21st September 2017, 8:28 pm

Cosmic73

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Ill check all the boost and vacuum pipes etc tomorrow morning.
Mike you make a good point about the MAF. Its connector is actually resting against side of the battery and vibrating away like crazy.
Its a standard PCV valve but i dont know if its fubar. Can it be checked without removing it?
Yeah black smoke was quite bad but only while it was stalling. disappeared the rest of time.
That rattle is just a loose bit if trim in the dash and shouldnt be a concern,
I dont have the tools to measure vacuum at idle but turbo seems fine with no boost issues.

7 Re: Intermittent erratic idle on 21st September 2017, 8:37 pm

mike74

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Just unscrew the pcv valve and see if you can blow through it or not (you should be able to suck through but not blow if that makes sense). Do you have a boost gauge installed, even the factory one?

8 Re: Intermittent erratic idle on 22nd September 2017, 7:06 pm

Cosmic73

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Seems to be running fine for now,
Anyway Checked PVC and all ok there,
Checked compression and got between 10 & 12 bar on all cylinders which is ok for a warm engine.
Sparking fine too, but I removed the plugs and they're well coked up. Also loads of black spatter coming out the back
Checked some pipes and connections which seemed to be ok.
Maf seems to be working ok.
Could this be turbo on way out?

This is the spatter it left on my wife's bumper.


YouTube video of exhaust is below, ignore the rattle , it needs fettling.
https://youtu.be/B09vlht-1Mg

9 Re: Intermittent erratic idle on 22nd September 2017, 7:16 pm

Gtirchris


Hmm, that's running really rich, try cleaning the maf with some electrical contact spray, check the Base timing and ignition amplifier is working properly mate.

http://www.guglielmimotorsport.co.uk

10 Re: Intermittent erratic idle on 22nd September 2017, 7:34 pm

mike74

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Yup, i had those symptoms with a dodgy maf. Ruff n rich running, soot the work's. Try cleaning maf and buzz it out Smile

11 Re: Intermittent erratic idle on 22nd September 2017, 8:12 pm

johnny gtir

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moderator
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Must just be video but smoke looked blue ? What happens when you un plug maf on idle

12 Re: Intermittent erratic idle on 22nd September 2017, 8:44 pm

Cosmic73

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Forgot to add that i also checked the timing and it's between the 1st & 2nd pulley notch.
MAF looks like a strong candidate and i cant help but wonder the vibrations going through its connector caused a fault. Since i moved it off from battery yesterday its been ok but smokey.
While it was running better today, i disconnected the maf and it instantly ran rough.
Ill give it a good clean and see how it goes over the weekend.

13 Re: Intermittent erratic idle on 22nd September 2017, 8:59 pm

Mr B

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gtir technician
gtir technician
Smoke does look a bit blue, is it using any oil ? is inlet tract to plenum showing lot of oil residue ?
Do you have wideband to monitor fuelling ?

14 Re: Intermittent erratic idle on 22nd September 2017, 9:34 pm

Cosmic73

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Exhaust smells of fuel not burnt oil and doesnt seem to be using any more oil then normal.
Ill check the plenum over the weekend. Ive no wide band monitir unfortunatly Sad

15 Re: Intermittent erratic idle on 23rd September 2017, 8:07 pm

nomad

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Admin
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How did you get on Neil any joy ?


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16 Re: Intermittent erratic idle on 24th September 2017, 1:39 pm

Cosmic73

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Was at Rally day yesterday so only managed to get under the bonnet today and tbh and cant see anything obvious. Plenum is bone dry and clean as a whistle, i cleaned the MAF and moved it off the battery. No signs of leakage or damage to any pipes. Starts fine and seems to run ok on the drive.
Im just about to take it for a spin with Ricky so we'll see what its like hot and after a bit if boost.
He's had a turbo failure in the past so might pick on the signs.
Fingers crossed its not
Neutral

17 Re: Intermittent erratic idle on 24th September 2017, 3:12 pm

Cosmic73

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Must've been the MAF, running sweet as a nut now, idling rock steady, boosting as good as ever and no smoke. Hope thats it for now

18 Re: Intermittent erratic idle on 24th September 2017, 4:29 pm

nomad

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Glad it's ok mate .... nothing worse than the feeling of eternal doom lol ...


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