Evo 7 GT-A Flashing CEL

[Babylon6]

Hi. Swapped gearbox on my GT-A and ever since, when I turn key in ignition I get the CEL flashing out 55. Once I turn engine on it goes to a solid light. I thought you had to ground out a pin on the OBDC plug to see this?

If I stick a basic OBDC fault code reader on I do not see P0505 but I do see P0300. I can clear the P0300 but it comes back as soon as I start the engine. This might be a red herring. Car doesn't feel like it is missing.

I have cleaned the stepper, checked its circuits and tried a new one. No deal.

Only other thing I have done is take rocker cover off to get it painted. Wondering if this could be a coil pack thing? Again no misfire ...

I have some idle hunting going on once engine is warm but I think that is due to ECU being reset by me when I swapped gearbox.

Has anyone come across this before?