Violent surging on over-run - closed throttle

[blu16v]

Hi guys, been lurking on this forum for some time now while i have been getting my Ebay valver ready for MoT - new front suspension, antiroll bar bushes, front brakes setup off an early MK3 for the bigger discs, new rear caliper, various new brake pipes etc.

Just picked my '86 valver up from MoT station and it is suffering from violent surging on closed throttle, any ideas welcome. It passed  so the emissions must be OK, but wonder if he has screwed the mixture to get a pass.

It has been stood around with little running for about two years. As you are a knowledgable bunch i thought i would run this past you before i did anything.

Thanks for your time

[Gambit]

only closed throttle what are the rev's sitting at? sounds like your closing the throttle but the rev's aint dropping?

[Ant]

Could this be an ISV problem?

[Gambit]

aye something to do with the ISV operation

likely to be either caused by an air leak or a duff ISV control unit which is usually caused
by a duff throttle switch which fries the ISV control unit.

[blu16v]

Thanks for the quick response guys.

Gambit, sorry to be pain, could you elaborate on the ISV, what is it? what is does?

Thankx

[Gambit]

its the Idle Stabilisation valve. basically controls the idle.

here's a pic of it in the engine bay just sits above the dizzy with an electrical connector on the back of it.
ISV location

[blu16v]

Thanks guys, i'll check it out and let you know, will probably be a few days, i'm supposed to be on garden watch/renovation/new path/cut the garss etc.

[rubjonny]

If it has a throttle switch (were they only on digi models?) check it clicks shut when you release the throttle, and test it with a multimeter to check it is working correctly.

[Gambit]

it does have a throttle switch.

PM deefadog - he had a post on here a while back about all this. it will explain evverything you need to know about the ISV control circuit

[monzablue16v]

pls post up here when you find out my isv needs an overhaul me thinks