I have a 98 gtp. For some reason the vacuum boost valve is stuck on open wen motor is running. Its suppose to b close right unless wen im giving it gas... Wat do I do to fix the problem... An will I get the whine bac if valve is workin right...?

large vacuum leak at rear hose from pcv valve

The spark plugs have absolutely nothing at all whatsoever to do with boost levels.

However; change them anyway because new plugs are always better. In the GTP, don't use the iridium plugs, use copper core. I highly recommend Autolite 605's, gap them to .055"

In the GTP, spark knock is a common, performance robbing issue because of the supercharging. You'll lose 5-6 horsepower for every degree of timing ****** that the engine computer will employ to prevent the spark knock. If you use copper core plugs though, this problem will be less likely because copper dissipates the residual heat much faster than iridium, so that only the electrode spark alone can be hot enough to ignite the fuel. The only other difference between the plug types is how long they last. Iridium plugs were the originals only because they last longer...they offer no performance benefit to the GTP.

Now on to your actual question.

There only a few causes for loss of boost pressure in the GTP, all of which are an easy fix.

Supercharger belt slip, disconnected or damaged boost bypass valve hoses, or maladjusted boost bypass valve linkage.

The easiest thing to do first is the boost bypass valve adjustment. This will produce results even if you DO still have belt slip or a leaking hose.

Locate your boost bypass valve. You will find it mounted directly in front of where the throttle body bolts into the intake plenum.
You will see that it is held in place by three bolts. Loosen them in this order; left, right and rear. You will find that you'll need a 4" extension socket to reach the rear one. Hold your socket on that one while you push down on the valve body. As you may notice the mounting bolt holes are elliptical, allowing for the height adjustment. You can use this as a visual reference for how far to push the valve down. You shouldn't push it down all the way, only about a half an inch will suffice.

What the adjustment does is reduces the amount of throttle opening needed to produce boost, by shortening the travel length of the valve lever that is attached to the throttle. When properly set, it will allow about 11 to 11.5 PSI at wide open throttle, or just short of wide open throttle. In any circumstance you may also notice that your GTP is a little quicker from a standing start after the adjustment.

SCAN VECHICLE FOR ANY SUPERCHARGER BOOST SOLENOID FAULT CODES.AND CHECK FOR LOOSE OR BROKEN VACUUM LINES GOING TO SUPERCHARGER BOOST SOLENOID THAT WILL CAUSE NO BOOST PROBLEMS.

Hello, the turbo models have what are called tumble generator valves mounted between the intake manifold and cylinder head. They close between a precalibrated temp range to improve emissions at idle in cold weather, as soon as you touch the gas pedal they open and do not close again unless the vehicle is turned off and restarted with in that same engine temp range. I have seen TGV units fail either due to carbon build up or the valve actuator motor fails, which is usually the most common. The most common symptom is loss of boost, it sound like your vehicle may have a slow TGV or one is starting to fail. If you have a boost gauge, and it's showing the boost is actually being lost, I would suspect the boost control valve which is usually mounted on left side of the engine compartment if you were looking at the front of the vehicle. It will be inside of a little metal bracket with an electrical connector and a couple vacuum lines going to it. I hope this info helps...(subytech1)...

Sounds like you have a stuck open egr valve. This will cause a HUGE vacuum leak and your vehicle will run poorly -- if at all -- until it closes. Your problem could be mechanical or electrical. I suggest having a technician look at it.

Check for a vacuum leak from the inlet and outlet hoses on the boost bypass valve and especially the boost solenoid.

I don't know much about Subaru but I expect the turbo wastegate is controlled by vacuum which is switched by the engine management system.

In the old days the turbo wastegate was normally closed and the manifold pressure was fed into a servo which opened the gate at the predetermined pressure.

The new way of doing things is to have the wastegate normally open and the turbo producing no pressure until the engine management decides the time is right and it switches a vacuum supply to a vacuum servo which then closes the wastegate. With this system the wastegate is constantly moving and so is unlikely to give trouble though the vacuum servo sometimes leaks and vacuum lines give trouble.

A fellow I know had a similar problem where the engine check light would light up and he would lose performance. In theory this was because of an overboost condition but the repair shop after fiddling around with it for a week fitted a new EGR valve to produce a cure.

If you have a GTP these engines use a hi output fuel pump. they use a fuel pump resistor located under the battery tray (look up from under the car) This resistor lowers the voltage to the fuel fump when not in boost mode. because of its locatoin it is prone to corrosion. if you bypass the wires and the engine starts and stays running replace the resistor

No leak, it may be time for a service to your supercharger. There is maintance that most people don't know about and the bearing to the supercharger's wear out and then has play. The bad things is with the play the lobes in the supercharger starts to rub against the housing and then the tolerace clearance is larger then when the car was new. Long story short, time to have your supercharger rebuilt before it fails and kills the engine too. There is an other way you can look in too, here is there web page http://cartuning.ca. Good luck

It is the boost bypass valve. The plunger will move with only enough throttle as it is connected to the throttle body.
The bypass solenoid you need is for the Eaton M90, the supercharger on your car. You can very likely get this part from zzperformance.