Yesterday i changed the ecu in my 94 wrx for one of the same type (a V9 ) so that i could send mine off to be modified , last night the car was fine and drove as well as it ever had done , but this afternoon the car started to missfire and hesitate when cold but clears when warm .
could this be a fault with the ecu or is it an un-related fault with something else?

 

any idea's anyone?

 

BTTT.

 

help please anyone?

 

I had a bad misfire when cold & it got worse & ended up all the time hot or cold on my 93 wrx.

turned out to be 2 knackered coil packs.

 

My 94 WRX occasionally has a very slight stutter/misfire just over 2000rpm. I only really noticed it after i changed the plugs to clears up a bad misfire further up the rev range.

Having already changed the plugs I'm guessing it's the coils next.