Rough idle.

[ScottMk2Gti16v]

I've got a similar problem with my 1991 mk2 gti 16v.   Bear with me as I'm not technical with cars.....

But mine does the same thing - it's not really a problem with it revving up and down - it's just when you come up to a junction and put the clutch in the revs drop down to about 300 and it stalls unless you give the accelelator a little flick.   Not sure the name of it - but there's a screw beside the throttle cable under the bonnet - turning it increases/decreases the air flow I believe?   Every other day I have to unscrew it some more as the idle speed keeps dropping - seems the screw is tigheting by itself therefore making the idle speed drop - am I making sense?   Is it just a faulty screw or a faulty part?

Sorry for the vague descriptions....I'm a bit of a newbie to parts and technical knowledge...but learning quick...

[snake16valve]

Hi Scott, there should be a locking nut on the screw that you are talking about.
Once you have set the screw to a position that it is ticking over fine then all you do is lock it in position with the nut.
It sounds to me that you haven't got the nut on the screw thats why you have to alter it every other day.
It is coming loose with the vibration of the engine.

I hope this helps you a little Scott.

[ScottMk2Gti16v]

Thanks for that - I'll have a look at it in the morning. I'm pretty sure there isn't a locking nut on it - the screw just goes directly into the hole.

I mentioned in my original post that it's to do with the air flow (I think). Any chance you can confirm to a non-techie the proper name for this part and what it's job is.  i.e. turning it increases air flow into the engine...which does what?   If I had to get a new locking nut what part would I ask for?

Am I right in saying the idle speed should be about 1000rpm?

Cheers for your help,
Scott

[snake16valve]

Hi again Scott.
I am not much of a brain box either so i cant say what it does. To be honest i think it is summit to do with the engine idle (tick over).As for the nut that you need just get one from any scrap yard.
As for engine idle anything around 900rpm - 1100rpm is OK.

cheers again and good luck m8.

[Gambit]

the idle screw doenst need a locking nut. you just need to replace the wee rubber O-Ring on the screw - this is what gives it a tight seal

you can get replacement O-Rings at any local motor factors shop for about 50p

also, the reason its stalling approaching junctions etc is because the CO% is not set correctly - there is a guide in the maintenace section.

[rowlers]

I've also had this prob when i first got my valver about 2 years ago. got the CO set  get 40MG!)spot on, cleaned the isv etc... still done it more so when engine really hot.

I cured the prob with a new hall sender from eurocarparts (about £30) and a new ISV control module off ebay for about a £1! It still does it but only about once a month.

Mine is also running very lean at the moment - about 0.8% CO at last MOT (must be why I 40 MPG ). but will be set up very shortly when my new head is fitted anyway.

[ScottMk2Gti16v]

the idle screw doenst need a locking nut. you just need to replace the wee rubber O-Ring on the screw - this is what gives it a tight seal

you can get replacement O-Rings at any local motor factors shop for about 50p

also, the reason its stalling approaching junctions etc is because the CO% is not set correctly - there is a guide in the maintenace section.

Thanks for that I've have a look into it.   CO% guide - is this what you're talking about? http://www.golfgtiforum.co.uk/index.php?topic=31611.0

PS - what does CO% mean?

[Gambit]

its just simply setting the fuel mixture - its how its measured

this is the link you need
http://www.golfgtiforum.co.uk/index.php?topic=22031.0

[snake16valve]

Hi Gambit.
Can you tell me what breather hose to pull off ?
thank's.


 (after the engine is at temp), pull off the breather hose and block the airbox hole.

[Gambit]

the black one that is going into the top of the airbox lid - u can see it on your pic running from the airbox underneath the alternator bracket to the front of the engine block