ISC - broken check valve - which symptoms ?

[Kristian_Wraae]

I think my check valve for the ISC valve is broken. I can both blow and suck air through the valve. On my buddies Supra it is only possible to blow air through the valve (from the outside to the inside of the plenum).

What would be the symptoms of a broken check valve?

When does the idle check valve close during normal operation?

Do the water lines have any effect on the operation of the check valve?

 

[jdub]

The check valve is there to prevent boost pressure from escaping via the ISCV...the NA 7M does not have it. It only functions under boost. The coolant lines have no impact on it other than to prevent ice under certain OAT/humidity conditions.

Symptoms would be the same as any boost leak...yours is FUBAR and needs to be replaced.

 

[Kristian_Wraae]

In which situations is the ISC valve closed? I belive it is actively closing and open by default? Well at least mine is open when the engine is turned off.

My ISC valve is very dirty, most likely because it keeps getting exhaust fumes from the EGR. What should I use to clean it?

 

[jdub]

It never closes at idle, otherwise the motor will die. The only time the ISCV is active is when the ECU is in idle speed control (IDL on)....to be honest, I don't know if it closes above idle or not. When the engine is running with no boost, it really doesn't matter since the ISCV uses metered air. Under boost, the check valve blocks the ISCV air path.

When the engine shuts down the ISCV steps full open to facilitate the next engine start.

To clean it, remove the step motor from the housing...3 screws...be careful with the thin, round gasket under the motor. Clean the valve stem with brake cleaner and a wire brush. Clean the housing and valve seat the same way. Reassemble, again, careful with that gasket. Get a new ISCV gasket and donut gasket for the check valve.