New problem sign pointing to idle valve!!

[Bigdunc]

hi guys i finally got my car to give me decent mpg after changing some sensers and fuel mixture, but recently after a 20mile run and motorway speeds the engin was cutting out when stoping, the revs were droping to low and engin cutting out.

things ii have tryed,
1. i unplugged the idle valve and sprayed it with carb cleaner and left to soak for 5 mins then put back
2. changing the idle screw on the throttle body
3. ajusting the mixture a tad just encase was to weak

now after all that still no joy engin still cut out after giving it some revs

so i unplugged the idle valve and set the idle on the throttle body up so engin stays idling without valve running and car seams ok now so im guessing it the idle valve

is there any more tests i can do to be 100% sure as they ant cheap to buy

Thanks

[raferackstraw]

to clean isv mate you nee to take it off and spray in carb cleaner, cover holes and shake, repeat until clear liquid comes out, then give a short spray of wd40 allow to dry out and refit. if you refit straight away you need to run engine at 1500-2000 revs for 5mins or so.

also check the switch on throttle body is working, you should hear it click when the throttle is closed.
also check overrun cut off valve, the grey thing below the air intake tube, remove it and clean it out with carb cleaner

other things to check are all vacuum pipes, best to replace, they can look ok but can be perished below cloth cover.
check injector seals are all good
clean out throttle body

isv should buzz on turning ignition prior to starting, if you unplug isv with engine running revs should plummit or cut out
other thing to check is isv controller behind dash
you didnt say whether 8v or 16v, these are what i did on my 16v

[Bigdunc]

i have a 8v gti

[raferackstraw]

ah, you can still do those checks, im just not sure where related components are, but first up remove isv and clean as i said 

[Sam]

Isv fo sho. Mine was well bunged up, to be honest it sounds like it couldnt be much else

[weazgti]

Stick a mk3 one in your pocket up the scrappie

[Bigdunc]

are the mk3 ones more reliable??
I have soaked the idle valve in carb cleaner blocking one of the holes and leaving to soak but come out clean after a good soak so its pritty clean valve, so will test again later, car seams to run better when warm without the valve plugged in just needs it for a cold start. would poss a idle valve from a vr6 be better?

[raferackstraw]

isv should operate on a closed throttle when throttle lever hits the micro switch iirc, this then operates the isv control circuit, it maybe worth looking at switch and voltages to it. the wiring can break due to heat n vibration.
if i unplug my isv with engine running  the engine stops

[Bigdunc]

if i unplug valve with engin running it use to stop but i upped the idle screw so engine runs without it on as engin kept cutting out. the bit on the throttle body makes a clicking noise and wires look ok. but i will get them checked out this week.

[raferackstraw]

pm rubjohnny mate  im sure he will point you in the right direction