Most likely one of the components that feed the PCM or that the PCM controls is malfunctioning. Engine bucks and the check engine light came on. I have a code 211 read out. Cleared all codes now the only code is 157 MAF sensor low voltage. 998-hardcode fault confirms that it is not the ignition module.
All sensors seem to check out ok.
Computer seems to always go into open loop. Code 211 is a profile ignition pick-up that means anything in the ignition system. Since you have eliminated the ignition module, try replacing the ignition pick-up coil. Code 998 merely is telling you that some hard codes have been set in the computer. A plugged catalytic converter can cause similar problems to the ones you are having.