picked up a sti for my brother thursday,brought from an importer.car has suddenly developed a missfire,it happens when the car is under load,runs perfect if you dont bring the boost in to much.
I am wondering if its to do with decat.It started shortly after fitting full h&s decat system,maybe coinsedence!
The car is a p reg and is 100% standard,well appart from decat now.Its only done 37k and is truly mint.
Is it likely to be coil packs at 37k.
I talked him into sccob instead of bmw and now this happens.doh

any ideas any1

 

May be a boost solenoid common problem boost spikes and then u get a full cut