Alright so I was running a set of Honda OEM Prelude SH platinum plugs, switched them out for a set of just regular OEM H22 plugs, not platinum. I've noticed seen then that when letting off the throttle once the car drops to about 4K RPM and below the exhaust starts popping pretty loud all the way down the RPM range.

All in all I think the car just runs shitty in general. I've got alot of fuel pulled out on the VAFC but the car still seems to run very rich and blows a decent amount of soot at full throttle.

I don't have EGR as this is a swap, also I have a Idle Air Control Valve code that won't go away. I orginally had a problem with my Fast Idle Thermo Valve but since replaced it and the car idles normal, however the code won't go away. I've tried reseting the ECU, yet the code remains.

The specs are:
JDM H22 w/ P13 OBD1 ECU
OEM Honda plugs
Header, no cat, no resonators

Any help is appreciated. Thanks.

 

Make sure the IACV is wired up and plugged in correctly, and try cleaning it too. As far as the misfiring, check ur spark plugs, they'll probly be pretty black, and wipe off all the black crap off of em. Has the car only been backfiring when since u switched out ur spark plugs wires? Make sure they're connected to the right cylinders on the dizzy and on the valve cover, and test the resistance between each wire to see if they're good. Should be around 18 ohms i think, if i remember right.

 

Plug wires are hooked up correctly. This has only been a problem since switching the spark plugs (not the spark plug wires) The plug wires are also NGK's and fairly new at that.

IACV is plugged in, I believe I cleaned it when I took the unit off in search of the cause of the problem. Don't know much about wiring, definetly not a fan of it thats for sure.

 

The first thing I would inspect for very close is an exhaust leak, it may be very small. Put the car in the garage at night, rev it up and watch for fire (backfire) light under the car or in the engine bay, if it is just out of the normal tailpipe then it is just because you are too rich and sucking in fresh air (O2) to burn the unburned fuel, this occurs on decel with suction at the tailpipe (normal).

If your exhaust leak is at the manifold / head or another location prior to the cat then you are also sucking in fresh air for the O2 sensor to see and it will think you are actually lean and richen up the air fuel mixture making your black soot out the tailpipe.