GolfGTIforum.co.uk

Model specific boards => Golf mk3 => Topic started by: spikenipple on 11 March 2014, 19:21

Title: Can a faulty ISV alone cause poor fuel consumption?
Post by: spikenipple on 11 March 2014, 19:21
Hello MK3ers

My car (MK3 16v - ABF) is idling high at the moment; around 1400rpm unless I apply some load to the engine (stationary, slip the clutch a bit in 1st) at which point it idles properly until I rev it again. The trouble is that my MPG has gone totally to sh!t, eg. 18MPG on the 13 mile route to work...

Can the ISV cause this if it's faulty?
I've replaced the temp sensor as I thought it might have been overfuelling - no difference.

I can't seem to find an air leak anywhere, and I can't hear one either.

Any ideas?

Also, does anyone have a diagram of the entire air & vacuum circuit for this car? The two tiny outlets on the filtered side of the airbox don't have hoses attached, and the little hose union on the top of the throttle body is blanked off.
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: spikenipple on 12 March 2014, 11:25
Anyone?  :sad:
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: Shizzle on 12 March 2014, 11:56
Not sure if this helps or is just a coincident to other factors at the time but when i had bad idle i used so much fuel on stop start journeys after cleaning and sorting the air leak it made a difference not huge but noticeable enough and idle was much better.


I used petrol to clean it and some RTV to help seal as both seals i had were not is best shape.

Also changed spark plugs at same time not that the old ones were really bad but for £12 i thought i would change them.

Also check your air sensor or intake pipe make sure it all ok wires not broke this caused similar thing on my car for some reason both wires had snapped off  :undecided:.
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: Len on 12 March 2014, 12:42
High idle does suggest a faulty vacuum hose, so check all of those.
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: Shizzle on 12 March 2014, 12:58
Especial on on back of inlet manifold next to throttle body did a clutch on my car other day some how cam off and car just kept stalling after revving up so simple so annoying.

I could imagine a small split in this pipe would cause a lot of issues.
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: spikenipple on 12 March 2014, 16:36
Not sure if this helps or is just a coincident to other factors at the time but when i had bad idle i used so much fuel on stop start journeys after cleaning and sorting the air leak it made a difference not huge but noticeable enough and idle was much better.


I used petrol to clean it and some RTV to help seal as both seals i had were not is best shape.

Also changed spark plugs at same time not that the old ones were really bad but for £12 i thought i would change them.

Also check your air sensor or intake pipe make sure it all ok wires not broke this caused similar thing on my car for some reason both wires had snapped off  :undecided:.

Cleaned what??

I'll check the wires too, hadn't thought of that. No fault codes on the ECU though  :undecided:

Any suggestions on a diagram of the air/vacuum system for this car?
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: Shizzle on 12 March 2014, 16:55
This it what i cleaned with petrol

https://www.google.co.uk/search?q=ISV+golf+mk3&source=lnms&tbm=isch&sa=X&ei=15AgU9vkFvOu7AbYyIHgAg&ved=0CAcQ_AUoAQ&biw=1280&bih=864#facrc=_&imgdii=_&imgrc=2vv_ks1xjCRlPM%253A%3Bwyn9wQ1GwYvzJM%3Bhttp%253A%252F%252Fimg694.imageshack.us%252Fimg694%252F4507%252Fmk2isv2wire.jpg%3Bhttp%253A%252F%252Fforums.vwvortex.com%252Fshowthread.php%253F4639318-FS-Idle-valve-stabilizer-for-MK2-ISV-2-wire-with-3-pin-thin-kind%3B1394%3B2224
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: xionsolaris on 14 March 2014, 20:52
that valve is quite expensive luckily the previous owner replaced mine with a new one at 80k
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: spikenipple on 14 March 2014, 20:55
Alright for some  :grin:
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: Len on 17 March 2014, 12:21
Standard airbox?
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: spikenipple on 17 March 2014, 18:13
Yeah. I'm using the airbox that I took from my previous valver, to which some tit drilled the TOP of the airbox so it's covered in tape at the mo. It's sealed though.
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: Len on 17 March 2014, 20:50
Was just thinking of the two vacuum pipes that go to the airbox was all.
Title: Re: Can a faulty ISV alone cause poor fuel consumption?
Post by: spikenipple on 17 March 2014, 21:03
Where do they go?