Amarin suggested my high idle issue after W.O.T. and max boost may be related to the turbo waste gate valve. I pressure tested the valve and found it leak down and closed as soon as pressure was released.
I tested a spare waste gate valve I had and found it held pressure until physically disconnected the air hose from the diaphragm
Does this mean the diaphragm is bad?
Something is telling the Idle Control Valve to stay wide open even after throttle is released to idle.
ECU, TPS and ICV have all been replaced and the wiring harness has been check without fault.
What do you experts thinks about a new waste gate valve?

John

Hello,

Just additional info. The Bosch waste gate valve in Volvo turbos is the compressor-bypass type (CBV). It vents excessive pressure back to the intake hose during idle and foot-off throttle changing gear time. It doesn't vent off to outside atmosphere as the blow-off type (BOV).

Please refer to this Volvo turbo page:
http://people.physics.anu.edu.au/~amh110/blow_off_valve.htm

The CBV could also in need of adjustment.
Please refer to this page:
http://forums.swedespeed.com/showthread.php?104485-Wastegate-Valve-Adjusting

From your description it could be the culprit. If you have a spare one replace it temporarily before getting a new part. Also please check that your air filter is not clogged. Otherwise it can't vent off the pressure.

Hope this helps. Good luck!

Amarin.

Hello Amarin,

Your knowledge takes this months-old problem in a different direction.
I am very grateful for you taking the time to pass you knowledge onto me.
The website was very interesting and I printed in out for future use.
The turbo is a TD-04, water cooled and I will swap the waste gate valve as advised with my used one.
Additionally, I just remembered that I had to replace the lower half of the air cleaner box because all the plastic clip holders had snapped off. The Volvo supplied replacement had only one air intake hole that went into the right fender inner structure.
The air box I replaced had two, the second inlet being behind the right headlight. Could this be mimicking a clogged air filter and starving the intake for air?

John

Hello,

No. I don't think that could mimic clogged air filter.

In older models during very cold weather starts the car takes heated air from the exhaust manifold via the second inlet. A thermostat inside the air box switches the air back to the first inlet when engine's fully warmed up.

Hope this helps.

Amarin.

Your 94 does not use the inner air intake, that was for older cars with the preheat hose from the exh mani. Your car has the electric sensor/heater in the rubber air tube from airbox to turbo.
While you're in the airbox, make sure all the foam in the top is gone, it clogs up the amm. Some including me remove the foam insert in the bottom also.