EssDub
If your exhaust is flowing too well, you will likely find that you are getting the overboost issues that plague these cars.  Basically, the exhaust flows far too well for its own good and the wastegate simply can't cope with the gas flow, thus letting the rest go through the turbine, creating the excess boost.  The fix?  Either a big single external gate, or two smaller ones, one on each scroll.

If the vsv isnt the cause then this is very likely the problem. I have a ct26 with 3 inch dump and it will boost to 18psi. This is with no boost control, just the stock wastegate spring which is 7psi.
 
This is a fairly common problem when using a 3 inch dump and an easy way to tell if this is your problem is to disconnect your boost controller (including the vsv if it isnt already) so your just running the wastegate spring, limiting you to 7psi.
 
Then go for a drive and have a mate keep an eye on your boost gauge while you do a good pull. You should hit 7psi quickly and then, if your wastegate isn't able to keep up, the boost should continue to climb at a slower rate i,e creep.
 
If this confirms your issue then there a couple of options. Firstly as EssDub said you could install external gates, this will work but will cost $$$ and is probably a waste of money with a ct26 IMO. Another option is to reduce the flow of your exhaust system either by reducing the size from the dump back or putting in a secondary cat (higher cell count is better in this situation). This will be way cheaper then external gates but kinda defeats the purpose of using the 3 inch dump in the first place....
 
I would suggest tuning for the higher boost and make sure you have the enough fuel to cope!

Steve_A

EssDub
If your exhaust is flowing too well, you will likely find that you are getting the overboost issues that plague these cars.  Basically, the exhaust flows far too well for its own good and the wastegate simply can't cope with the gas flow, thus letting the rest go through the turbine, creating the excess boost.  The fix?  Either a big single external gate, or two smaller ones, one on each scroll.

If the vsv isnt the cause then this is very likely the problem. I have a ct26 with 3 inch dump and it will boost to 18psi. This is with no boost control, just the stock wastegate spring which is 7psi.
 
This is a fairly common problem when using a 3 inch dump and an easy way to tell if this is your problem is to disconnect your boost controller (including the vsv if it isnt already) so your just running the wastegate spring, limiting you to 7psi.
 
Then go for a drive and have a mate keep an eye on your boost gauge while you do a good pull. You should hit 7psi quickly and then, if your wastegate isn't able to keep up, the boost should continue to climb at a slower rate i,e creep.
 
If this confirms your issue then there a couple of options. Firstly as EssDub said you could install external gates, this will work but will cost $$$ and is probably a waste of money with a ct26 IMO. Another option is to reduce the flow of your exhaust system either by reducing the size from the dump back or putting in a secondary cat (higher cell count is better in this situation). This will be way cheaper then external gates but kinda defeats the purpose of using the 3 inch dump in the first place....
 
I would suggest tuning for the higher boost and make sure you have the enough fuel to cope!

I agree this approach.

Can anyone shed some light on this? When the shop was installing the electronic boost controller, I don't recall him doing this..

http://www.turbomr2.com/MR2/HowTo/AP...%20AVCR-02.htm

In this article it states "Cap both ends. You must securely clamp the cap on the wastegate actuator nipple, or you will experience uncontrolled boost (as I learned firsthand). Here's a photo of the rubber hose plugs I used, before they were clamped down:"

He didn't do this... Do I have to do this as well?

petmr2
Can anyone shed some light on this? When the shop was installing the electronic boost controller, I don't recall him doing this..

http://www.turbomr2.com/MR2/HowTo/AP...%20AVCR-02.htm

In this article it states "Cap both ends. You must securely clamp the cap on the wastegate actuator nipple, or you will experience uncontrolled boost (as I learned firsthand). Here's a photo of the rubber hose plugs I used, before they were clamped down:"

He didn't do this... Do I have to do this as well?

If it hasn't been done then yes you need to cap them. When you look at the wastegate what is happening with the second port? Is the hose to the T-VSV still connected?

Thanks... I'll need to have a look when I get home. From memory all he did was disconnect the hose from the wastegate and connected the hose for the solenoid and boost gauge. I'm confident he did not block it off... And yeah I think the hose to the T-VSV is still connected... really hope this is causing the issue. 

Yep just found another article form twosrus stating the same thing... http://www.twosrus.com/Articles/Installation_Instructions/MBCinstructions.PDF