High idle got me stumped

Hi Peeps

Bit of a weird one, my car idles at 1500 rpm, doesnt hunt and is a smooth idle. Ive tried adjusting the idle screw and 1500 is the lowest it will go..... that is unless you disconect the isv, then it happily sits at 900rpm but if you rev it fails to catch and stalls so the isv is needed.

So i figured the isv just needs to put into setup mode.... alas in setup mode it idles at 2500 rpm, and will not go any lower unless you take it out of setup mode..

I really cant figure out what is wrong, fingers crossed one of the kind peeps on here will know

Thanks Dan

 

What car/engine etc?

 

Haha sorry thats a pretty big bit of missing info.

Its an Abf in a mk2 jetta running kjet.

 

Nope, the isv control unit failed so whilst i found a replacement i upped the idle to stop it stalling, but now with a work control unit i cant get the idle down.

 

Sounds like the ISV is stuck open.

Have you had a look at 'rubjonnys' 16v set up guide, tested the temp senders etc?

 

Here's the original text I did about 12-13yrs ago..I feel old now.

The pics with my dirty fingers on don't seem to work anymore!! [sad]

 

I have tried to adjust the idle with the spade disconected but the idle climbs to 2500 and wont come down.

I too thought isv could be buggered so i tried another and problem still remained

I had a read throught the 16v setup guide originally which is where i learned of the isv setup mode.

Cant think if anything else it could be.

 

A long time ago.

I'm trying to picture how all the pipes,bits & bobs go on them. lol

 

I don't understand how disconnecting the red/black wire makes it rev higher, as i always thought that takes the power from the ISV, unless it's pulling air in from elsewhere?

 

I cant figure it out either, all my vacuum lines are good and im pretty certain its not getting air from anywhere it shouldnt.

 

How about the Y shape pipe the ISV connects to? All ok?

Does the throttle flap close fully?

Has the throttle stop been wound out?

I guess that must be all ok if if it idles at 900 with the ISV disconnected.

 

Yea all seemed fine when checking earlier, i will have a double check tomo after work but like you say its weird how it idles nicely with no isv :/

 

Okay i have double checked and all seems fine and dandy leaving me well and truly stumped!

 

Have you got the correct ISV?, the Digi1's look exactly the same but work differently (they are closed at 25% duty cycle, when disconnected they open again as a fail safe). Sounds like you have a G60 valve fitted?.

 

Well i have 2, one bought from a chap on here and tge other from when it was 16v kr and both do the same :/