Can a faulty ISV alone cause poor fuel consumption?

[spikenipple]

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.

[spikenipple]

Anyone? 

[Shizzle]

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  .

[Len]

High idle does suggest a faulty vacuum hose, so check all of those.

[Shizzle]

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.

[spikenipple]

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  .

Cleaned what??

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

Any suggestions on a diagram of the air/vacuum system for this car?

[Shizzle]

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

[xionsolaris]

that valve is quite expensive luckily the previous owner replaced mine with a new one at 80k

[spikenipple]

Alright for some 

[Len]

Standard airbox?