Mk2 Gti - Revs Drop Quickly On No Throttle

3102 Views 15 Replies 5 Participants Last post by Oisin, Jan 30, 2006

dealgan

Discussion Starter · Jan 23, 2006

Hi folks,
My mk2 gti 8v digifant runs well ; except when you take your foot off, in neutral, the revs drop so quickly it can almost die out. - it does the odd time, but not often.
e.g. Rolling to stop at a junction you are never quite sure if it will just drop to idle, or die.

I did notice that even when changing gear, the revs drop off quite quickly, as if the flywheel is lightened. (Mabye it is, I don't know !!)

I suspect some vacuum hose(s) or something along those lines.

Any ideas where to start ?

Thanks,
Declan

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Geo

· #2 · Jan 24, 2006

Clean your isv. That should sort it. Just take it off (2 hoses and a plug) and spray the inside of it with carb cleaner spray. Some people like to soak it in petrol overnight but I always found the carb cleaner to do the job fine.

If you don't know where it is then looking at this picture of my engine you can see just above the rocker cover in front of the inlet manifold you can see a silver cylinder-shaped part, that's the lad you are after

Hope this helps, let us know how you get on.

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Oisin

· #3 · Jan 24, 2006

while u have the carb cleaner out, you may ask well spray down the throotle body,
take off the large black pipe (going from the air filter case to the throttle body), then spray a small amount all round inside the throotle body whilst opening and closing the throttle, then get a ear swab and clean off heavy stuff, spray again, connect everything up and start her up, take her 4 a trash on the road.

other than that make sure your fuel pumps are good, or try changing ur fuel filter.
All the best with it.!

dealgan

Discussion Starter · #4 · Jan 24, 2006 (Edited by Moderator)

Great info guys. Thank You.

As I have to buy some carb cleaner .... what am I looking for .. It it actually called "carb cleaner" or is there a different name on it ?
- Is there a particular make/type I should buy ?

I'll report back if it worked or not.

Cheers,
Declan

johnny99

· #5 · Jan 24, 2006

Carb cleaner or carb and choke cleaner. All factors will have it.

John

dealgan

Discussion Starter · #6 · Jan 27, 2006 (Edited by Moderator)

OK, got some carb cleaner, took off the isv and sprayed liberally in both openings.

The revs dont seem to drop as quickly now, but if I rev to 2 or 3k then take my foot off, it still does drop below 700-800 and then correct itself again back to around the 800/900 rpm mark. The idle is steady. No hunting or anything.

Does that sound about right, or do I need to clean it more thoroughly ?

I didnt get any gunk out of it at all.

Mabye I should do a sound recording of it and let you hear it !! Might be easier than me trying to explain it !

Cheers,
Declan

EDIT: Just went for a quick drive to compare .... no difference at all

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VwDan

· #7 · Jan 27, 2006

Isn their a problem with a dodgy relay that causes this?

Bring her up to Lenard Wilson at Burt he wil sort ya out, if you need his number i find it for ya.

Geo

· #8 · Jan 27, 2006

QUOTE (dealgan @ Jan 27 2006, 05:35 PM) <{POST_SNAPBACK}>OK, got some carb cleaner, took off the isv and sprayed liberally in both openings.

The revs dont seem to drop as quickly now, but if I rev to 2 or 3k then take my foot off, it still does drop below 700-800 and then correct itself again back to around the 800/900 rpm mark. The idle is steady. No hunting or anything

That sounds like the way my car is all the time so it could be behaving normally. Maybe you should take a sound recording of it.

dealgan

Discussion Starter · #9 · Jan 28, 2006

QUOTE (VwDan @ Jan 27 2006, 08:13 PM) <{POST_SNAPBACK}>Isn their a problem with a dodgy relay that causes this?

Bring her up to Lenard Wilson at Burt he wil sort ya out, if you need his number i find it for ya.

Dunno about the relay .. must search for info on that.

I know of Leonard .. supposed to be very good with "anything german" !

Cheers, Declan

dealgan

Discussion Starter · #10 · Jan 28, 2006

QUOTE (Geo @ Jan 27 2006, 10:17 PM) <{POST_SNAPBACK}>That sounds like the way my car is all the time so it could be behaving normally. Maybe you should take a sound recording of it.

OK. I made a small movie clip showing the rev counter.
I cant get it any smaller than about 800K !

Video Clip (WMV Format) 820K

Oisin

· #11 · Jan 28, 2006

have you tried swapping parts from from another 8v?

try taking out the air flow meter and try it with one that works, thatll rule that out,

put it back,

then try swapping the fuel rail, if no different, try the ECU. or the connections on the ecu. Its trial and error.

I had bother with mine over xmas, where shed start but eventually conk out. After playing around like this it didnt take too long to find out it was the connections on the air flow meter.

Also try cleaning the timing screw in the throttle body, have heard it can do odd things when dirty.

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dealgan

Discussion Starter · #12 · Jan 29, 2006

QUOTE (Oisin @ Jan 28 2006, 09:53 PM) <{POST_SNAPBACK}>have you tried swapping parts from from another 8v?
No. I Haven't.

QUOTE (Oisin @ Jan 28 2006, 09:53 PM) <{POST_SNAPBACK}>Also try cleaning the timing screw in the throttle body, have heard it can do odd things when dirty.
OK. Cheers.

johnny99

· #13 · Jan 30, 2006

Timing screw ??

John

Oisin

· #14 · Jan 30, 2006

QUOTE (johnny99 @ Jan 30 2006, 09:15 AM) <{POST_SNAPBACK}>Timing screw ??

im not a mechanic!

What i mean is the screw for adjusting the mix on the throttle body!

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Geo

· #15 · Jan 30, 2006

The idle screw?

Oisin

· #16 · Jan 30, 2006

QUOTE (Geo @ Jan 30 2006, 11:43 AM) <{POST_SNAPBACK}>The idle screw?
Thank You

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