Can someone just give me a brief example and description of the blinking sequence I might expect when i do check the diagnostic. Say an error code for a faulty intake air temp sensor (Code 24) OR air flow meter signal error (Code 31)? Thanks.

HAve a look at the link below for some information on the procedure. It is for a Celica but its the same engine and basically the same ecu. Codes are the same also.
There are MR2 guides on the net somewhere but I found this one when I searched in 2 seconds etc.
 
http://www.toyotanation.com/forum/17-celica-forum/72740-gt4-3sgte-easy-mods-common-faults.html 
 
The bottom half of the guide above is specific Celica stuff so just read the first bit on error codes.

if you used the search function like i mentioned you would ahve found this
 
http://www.mr2australia.com/mr2play/tm.aspx?m=58447&high=error+codes
 
 

Thanks a bunch both of you. I'll post how it all went a bit later on.

Ok, so i ve run the diagnostic procedure and its error code 14: the ignition coil. There was no more error codes after. It just kept on repeating that one. Anyone know how to solve this??

Did the mechanic who installed the new bov plug the hole that is left over in the air filter piping? The stock blow of valve vents back into the black piping between the turbo and air flow meter.
 
From what I have read a code 14 can be stored if you keep trying to start the engine without success.
 
Other reasons for code 14 can include, faulty ecu, igniter, coil or wiring in between.
 

The pic below shows the where the stock bov used to connect to. Check to see if the mechanic has plugged the black air filter hose where the black metal bov pipe used to be. 
 

 

Well there is def an unconnected hole on the inlet going into the AFM meter, was that previously like that, i cant remember. All i know is the previous set up was with a plum back BOV feeding back into the intake. I will take a pic of the whole set up tonight and post it so you can inspect. As for the error code, I have been trying to start the engine quiet a few times, so maybe thats a possibility. The other night though when i unplugged the ecu the first time, it started straight away, but then the same issue. unplugging it again didnt help. What explains that?

Block that hole in the air filter piping and try and start the car?

Just keep in mind that whatever you block the hole with must not be able to be sucked through and into the turbo.
Just block it with your hand or something temporarily and get someone to start the car.
If that ends up being the problem you'll need something like this http://www.hpheaven.com.au/store/parts-accessories/info/1256/turbosmart-bov-25mm-hose-blanking-plug/?cat1=48&catid=0&page=1