Scirocco Register

Got the Idle speed down from 1300 to 950 last summer; cleaned metering head, air filter, throttle body. Ran lovely like this for several months.

Car was then laid up for maybe 4 months.

On bringing her out of hibernation the idle speed has now dropped to 200-300 but occasionally, usually after a brief period of high revs, the Idle speed will return to around 950 then when clutch depressed or car stopped and restarted Idle speed drops to 200-300...

Cleaned the metering head again, plenty of fresh fuel over 800 miles this year. Should mention that the screw to adjust Idle on throttle body is fully closed (due to previously reducing Idle speed)

Any ideas..? Sounds like something is sticking...

Saw the forgotten GTX resto thread and thought maybe a faulty microswitch. Bit expensive if it's not €45 + shipping

Thank you for help

Typically I often had to adjust my idle screw to get the right level as like yourself my car wasnt used frequently or if so was doing very short journeys..

She gets used pretty regularly. 800+ miles in last month...

Had a weird one this evening. Parked up with headlights on and Idle speed was hunting in a mesmeric fashion between 200 and 600. Turned the lights off, then on and idie settled to its regular 200-300 rpm

Gonna try bringing Idle speed back up to 950 with the screw and see if strange going ons persist.

Could be the rubber seal on the idle jet is old, hard and flat and letting in air or working it self lose over time. A new o-ring is pence so may be an idea to replace it?

Pictures... If the need to size of the o-ring let me know as I took some measurements.
My old one fitted and my screw used to work it self lose.


New one fitted.

Had a minute to check this out. O ring felt OK.

Business end of screw was encrusted with hard black stuff. Carbon build up maybe. The entire intake system was covered in it when I got the car.

Carb cleaner wouldnt shift it.



Stuck it on my mates burnishing wheel. Came up a dream.



Had the throttle body off, but impossible to clean the airflow channel inside casting...

Idle reset and hasn't wondered since.

mark1gls wrote: Thu Mar 03, 2016 12:56 pm Could be the rubber seal on the idle jet is old, hard and flat and letting in air or working it self lose over time. A new o-ring is pence so may be an idea to replace it?

Pictures... If the need to size of the o-ring let me know as I took some measurements.
My old one fitted and my screw used to work it self lose.


New one fitted.

Sorry for digging this up from years back mate, but do you remember the size of that o-ring? Will be slapping a new one on mine but don't have it to hand.

I did take some pictures of the size of the o ring but I can’t find them tonight, give me a day or so and I’ll see if I can find them for you.

Found the pictures, the I ring is rubber so tricky to get a measurement but it will give you an idea.

I did have to smear a little grease on mine to be able to slide it on.


Out side measurement



Inside measurement


Sent from my iPhone using Tapatalk

Meant to say thanks for this mate! Ordered a new o-ring and it's now on the idle jet. Hoping it'll help out idling issues when I get round to finishing off the current jobs and starting her up again.

Glad it was some help.
If you do find the idle screw moves and your idle speeds drops at any time you can wrap a bit of PTFE tape around the thread as I’ve seen a few do this, I’ve not had to on mine though.