what is normal iddle on sierra cosworth
my iddle is 1100 - 1200 rpm cold, and after that on normal engine temperature goes to a 1500 - 1800 rpm on iddle

 

Normal idle speed for a 4x4 is 900-950rpm, ~1200 when cold.

Your Idle Speed Control valve may be sticky, or you may have an air leak at the inlet manifold - either a split gasket or split hose.

 

i havent air leak because in boost my pressure isnt drop down, any other suggestions

 

If its just a little leak it will be enough to raise the rpm, but wont affect the boost.

 

from inlet gasket or, how can i understand easily from where is air leaking, what about coolant temp sensor

 

It would be worth giving the iscv a spray with carb cleaner then furniture polish containing silicone afterwards.
Things that can raise the idle speed include the CTS if engine thinks it's cold, so could check CO.
The engine relies on air, so try adjusting when hot and electrical loads turned off, the bypass screw on the throttle housing underside, if this doesn't have the desired effect, then I would look for air leaks.
tabetha

 

what is CTS
and what is iscv

 

what is CTS
what is CO
and what is iscv

 

CTS= Coolant Temperature Sensor (Blue colour sensor on inlet side at back of cylinder head underneath plenum is tricky to remove, believe is same on 4x4 as well)
CO= Mixture at idle given as a % value
ISCV= Idle Speed Control Valve (On inlet side of engine on top of throttle body, has white top with wiring plug, remove this by depressing clip it is then held in by two screws either side then a ring lifts off, the valve can then be removed.

Tip first try removing the wiring plug on top of ISCV with engine running if idle speed drops it shows it is being told to open this much in which case probably the CTS)

Martin

 

i turn off air temp sensor and Idle Speed Control Valve , and there is no difference
cold start 1200rpm and i turn off gauges end when engine go work temp is on 1500rpm
after that i turn on air temp sensor and Idle Speed Control Valve and rpm is the same

 

maybe wrong l8 chip, or it cant effect on idle rpm

 

if you pull the plug from the iscv and nothing changes, i would bet on an air leak somewhere at the inlet.

 

it could be Coolant Temperature Sensor or bad l8 ecu chip, i dont know

 

You just need to adjust idle set up.

1
Engine in good temp, disconnect idle valve.

2
Adust screw rep.1 to obtain a good idle speed (850 / 900 rpm)

3
Reconnect idle valve.

 

But if theres is no iscv connected, than the ecu cant give any signal to the iscv (even if it would be a false signal) so the engine is running on it idle rpm, that can be adjusted with that srew under the throttlebody


edit: @above...thats what I tried to say ^^

 

i havent scew rep on my sierra cosworth

 

the problem was fixed, thank you

 

What was the problem then?

 

Adust screw rep.1 to obtain a good idle speed (850 / 900 rpm)

 

No need to unplug ACT, if you unplug ISCV and idle is same then most likely ISCV is sticking, have you tried taking out yet and cleaning and lubricating?

If still same after then you have air leak somewhere.

Martin

 

Digging up a old thread, but adjusting base idle and reconnect iscv cured the high idle?

 

i only abjust base idle and everything was fine for me