Author Topic: Cold start running  (Read 917 times)

Offline RyanC

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Cold start running
« on: December 04, 2016, 07:45:04 pm »
Hi guys,
From cold I have a bit of an issue. I had a very uneven idle when hot, this turned out to be the idle screw out to far. Unplugged blue temp and reset the idle was spot on.
Car runs fine when at operating temp now but now from cold start up the idle is at a normal level 100rpm ish, no increase at all if you rev it up it's okay but returning back to idle is you let off the throttle too fast it will cut out. It's like the aux air valve isn't working.
Any good ways to test this? I know it's controlled by temp, 12v ingnition feed for heater.
Or any other ideas? 
This only happened after adjusting idle screw in to correct position
Cheers

Offline Yoof

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Re: Cold start running
« Reply #1 on: December 07, 2016, 02:49:14 pm »
What's the idle speed when hot, and what is it when cold (assume 100rpm is a typo).

Remove the ISV and test it on the bench, it's only acting as a bypass valve. Once you've cleaned it and are satisfied it's working, check the stops on the throttle body are correctly adjusted, also check the idle switch is engaging at the correct time.

Check for vacuum leaks too - injectors seals are a favorite.

Does the car happily go into service mode?

If all that checks out, it could be something like plug fouling (especially if you're not running it for long between starts).

Offline RyanC

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Re: Cold start running
« Reply #2 on: December 07, 2016, 06:29:38 pm »
Thanks for the reply. Idle hot or cold is 1000rpm or just under, once warm it runs fine, just 1000rpm idle speed when stone cold is not enough I guess.
 
Okay I'll remove it and check it. How do they actully work? sticking 12v up it won't do a lot will it? As it uses the temp of the water pipe to move it? I thought the 12v was just heat it and help it move when the temp changes?

I will check for leaks as well this weekend.

So adjust idle switch so it clicks open as soon as the butterfly moves?

Service mode seems to be fine. Engine runs steady and timing holds the same position.

I'll check the plugs also

Thanks

Offline Yoof

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Re: Cold start running
« Reply #3 on: December 07, 2016, 08:15:35 pm »
It's just a bypass valve - nothing fancy. There's an adjustment screw on them too.

When the engine is cold (high idle condition) the ISV should be open slightly (you can see light through it)



(Picture stolen from internetz)

When the engine is warm (normal idle condition) the ISV should be closed.



The ISV closes as it heats up - it has an internal heater and on the Polo is also mounted on the water pipe behind the block, so will have some conducted and radiated heat.

For the bench test just use the heating element and see if it closes up.

If you need a new one, I think some of the earlier K-Jet Golfs ran a similar valve.

Hope this helps

Pete

Offline RyanC

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Re: Cold start running
« Reply #4 on: December 07, 2016, 08:22:27 pm »
Nice one thanks for the info you can get them for VW heratige new so if I need one I'll get a new one
Thanks

Offline RyanC

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Re: Cold start running
« Reply #5 on: December 11, 2016, 07:32:48 pm »
All fixed! Idle valve was solid. Runs spot on now.
It runs quite rough when cold to though. Smooths out pretty fast but it's just lumpy if the use throttle at any point from cold
Any ideas?

Lastly when unplugging blue temp when it's up to temp to adjust idle or timing I don't really get any change to engine revs at all nothing really happens.

Offline kwijibo_coupe

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Re: Cold start running
« Reply #6 on: December 11, 2016, 08:53:38 pm »
Mine hates a cold start, runs lumpy as fuck for about 30 seconds then smooths out. Pretty much just accepted that is how it is.
Dunno if it has anything to do with the cam in it, I'm running a Schrick 268/268.

When unplugging the blue temp the revs should rise to about 1200rpm if the timing and idle are set right. But I've usually found if the ECU isn't happy with something and you unplug the blue temp the engine just stalls out. So if it isn't stalling out maybe just the idle itself needs brought up a tad?

Offline RyanC

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Re: Cold start running
« Reply #7 on: December 11, 2016, 09:33:07 pm »
Yeah I've got the same cam I think that's what it is tbo.

Should you set revs to 1200 rpm then with blue temp unplugged??

Offline RyanC

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Re: Cold start running
« Reply #8 on: December 11, 2016, 09:52:53 pm »
Just read the blue temp can cause cold start running problems and fine when warm so I'll check that too for the lumpy start up. 

So I've just read that idle needs to be set at around 1200 with it unplugged is that correct?
Ive always set mine to 1000 maybe that's where I'm going wrong here
A bit of trial and error to get it just right though.

Will have anouther play next weekend!

Offline RyanC

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Re: Cold start running
« Reply #9 on: December 11, 2016, 10:28:07 pm »
https://www.polog40.co.uk/forum/index.php?topic=1227.0

If anyone can shed some light on this topic that would be awesome I'm not using a genuine vag sensor I'm running a hella one so good quality but maybe the cold readings are not what the ECU want to see

Offline kwijibo_coupe

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Re: Cold start running
« Reply #10 on: December 12, 2016, 12:16:00 am »
I have my idle set to 1200rpm with the blue temp unplugged, drops to about 900rpm with it plugged in.


Offline Yoof

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Re: Cold start running
« Reply #11 on: December 12, 2016, 07:41:05 am »
Lumpiness akin to 1341cc motors is cold running clearances of forged Pistons that you've fitted.

Offline RyanC

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Re: Cold start running
« Reply #12 on: December 12, 2016, 06:10:25 pm »
Ah very true, Thanks for the info Pete :)