I recently rebuilt the engine and installed a new cylinder head as the old one was toast. I have replaced the IAC valve, MAF sensor, ect sensor, both coil packs, new plugs and wires. Everything I have changed to this point seems to have an effect but has not fixed my issue. My issue is that when I cold start the engine idles very rough and more often than not stalls. If I give throttle it will backfire through the intake but usually continues to run. If I can ever get it warm, say just above the cold mark on the dash, it seems to idle fine but will sometimes stall if I hit the throttle the let off and if it doesn’t stall the rpm’s generally drop low then it recovers. I just now got a code po340 and po350 after weeks of it running like this and if I clear them they come back almost instantly. I’m not even sure where to start. I will mention that it seems more apt to stay running at cold idle if I unplug the front coil. Any help is greatly appreciated. I have also smoke tested and cannot find any vacuum leaks.