High Idle

[adavy]

I have recently changed all my plug leads as No8 cylinder lead was burnt through causing misfire. Replaced with OE leads and heat socks. Since then I have a high idle at about 1200rpm (used to be 850rpm). I've cleaned stepper motor etc. Tried to set the base idle clamped hose etc but the plenum screw wont let me go as low as 500-600 rpm (it wont turn any further.) My idle when warm is 1200. Sometimes goes up to 1800 when coming to a standstill and slowly returns to 1200 where it is completely stable.

Any ideas?

[blaze_away]

Most likely you have a vacium leak. Only way to be sure of finding it is using a smoke generator

[Belle427]

As above, it's not ideal but you can use carb cleaner spray to find leaks but advised to do on a cooler engine.
Check all your hoses are connected ok, especially the small take off connection for the fuel regulator that is on the stepper housing if you have been near that area.

[Classic Chim]

If you have removed the stepper for cleaning check for leakage there too.
There should be a fibre washer and I tended to use some plumbers tape on the threads to be sure.
Don’t do it up to tight as you can break them.

[adavy]

So I found a couple of small vacuum leaks (base idle screw and distributor vacuum) sorted them but still have same problem. When hot idles at 2000rpm gradually coming down to 1000rpm.

Whats next - new stepper??

[Belle427]

What happens when you clamp the rubber hose to the stepper as if your attempting to set base idle?

[adavy]

Revs drop to about 800rpm and base idle screw wont go in any further

[Belle427]

Still sounds like its pulling air in from another source if the bypass screw is totally closed, strange it only happened with the plug and lead change though.
try clamping off the rubber hoses connected to the plenum one by one to see if it makes a difference, breathers, servo hose etc.
from memory there is dizzy vacuum, fuel pressure regulator, breathers, servo, carbon can.

[Sardonicus]

You haven't rotated the dist when you changed the cap and leads by accident loose clamp etc ? Over advanced ign timing this will raise idle speed

Edited by Sardonicus on Thursday 17th August 17:10

[adavy]

Well that was a saga!!

Found a few vacuum leaks - sorted them

Cleaned stepper motor and housing

Still the same and couldnt set idle speed.

So got roverguage and the lead. fault on ecu coolant sensor. Found the sensor and, guess what, the connector had fallen off - now it sets just under the ht leads!!

All sorted! Thank you all for your help.

[Belle427]

Oh well, at least it's now sorted.

[blitzracing]

An open circuit temp sender would represent a very cold engine so the idle will be raised as if to start the car I suspect.