Purchased a 2002 WRX STI at the weekend.

I noticed when driving it trying to boost from around 4k-5.5/6k the boost gauge needle flys back and forward a few psi and the car sounds like a rattle snake?? is this normal? what could be the issue?

Also tonight the EML light came on.

I will find out the code tomorrow.

Another question is, The car is remapped for v-power with race dynamix, I've run the car home some 300-400 miles on normal 95 ron unleaded? could this have caused any damange or issues relating to the Boost or EML light?

 

You've answered your own question.
DO NOT use 95 in a car mapped for V-Power.

 

Car has been fixed by local garage, EML light was due to a dirty ICV. how ever the boost still flaps back and forth and makes the rattle snake sound and there us no vacuum leaks??

any ideas?