I recently replaced the B18C1 I was running in my 4/10 mile oval dirt track racecar ('95 Integra RS) for an OBD2 JDM B18B (VTEC engines were outlawed after I won a race). After installing the B18B things have not been right. The engine will run great at times, but it never seems to sound quite right at idle, and it sometimes acts as if it is running on 3 cylinders. I changed all of the following with new parts:
- NGK spark plugs
- OEM wires
- OEM cap
- OEM rotor
- fuel filter
- fuel pump is a Walbro 255 lph

I also checked the following:
- different distributor
- different P75 ecu
- cleaned all grounds
- checked and changed the TPS

In a last ditch effort I threw an automatic P06 I had laying around in. It had an interesting up and down idle, but it ran perfectly. My question is, what would make the engine run correctly with the P06, but not the P75? I am truly stumped, and I need all the extra power and rpm range I can get as this track is quite fast. Any help would be greatly appreciated. Thanks!