Idle woes

[mr burns]

Hi all
 having a nightmare with the old car at mo fix one problem up pops another  I, m getting the old erratic idling thought I,d fixed it with a used isv off flebay put it in ran fine til this morning back to revs up down again, took the isv into work and got it tested by putting 12volts through it on the bench and it opens and closes fine so my question is can I rule out a duff isv or does it do more than just open and close and if it is ok I,ll look at the hoses for air leaks do they come as a set and what do I ask for lastly does the idle screw have an oring on it can I buy one or do I need to buy thescrew as well. Hopefully I,ve covered it all if theirs anything else I should do or look at please let me know.

Thanks

[rubjonny]

what engine is it?
the valve inside opens and shuts at varying frequencies to regulate air flow, if it opens when you put 12v on it that suggests all is well. does it buzz with the ignition on?

[mr burns]

Hi yeh it buzzes ok it's mk2 gti 16v 1992

[rubjonny]

have a good look at your throttle linkage. 16v are prone to the top bit gumming up which means it doesn't always hit the idle switch. take top 13mm nut off and clean/grease. when rebuilding take care not to catch the spring in the plastic washers, that'll make it sticky again.  it can also cause problems if your throttle cable is old n worn. they start to fray up which means they get sticky and hold the idle switch linkage open. gsf cable is cheap and makes rthe world of difference to the feel of the car. give it a quick spray of silicone lube down the cable sheath as well, some gsf cables are a little dry.

if all that is fine, check the idle switch adjustment. if it doesn't click when the throttle is fully shut, undo the scres and move it till it does. sometimes you might have to bend the end of the linkage a tad before you can get it to contact the switch

[mr burns]

Thanks all for the replys I think I,ve found the cause it looks like the idle screw, I took it out gave it a clean and now all seems fine. I will keep my eye on it as maybe a new one is needed can, t see them being that much to buy.

Thanks again