1993 R1. Pettit built street-ported engine(less than 200 miles), pettit high flow twin turbos, ported intake manifolds, aws blocked off, egr deleted, air injection pump deleted, full 3 inch exhaust, pettit heated O2 sensor. The car ran fine for a few days, the idle was coming up as the seals seated. 2 days ago I adjusted the idle back down to were it was supposed to be. Yesterday on the way to work the idle took a crap and it started idling around 600rpm instead of the 850rpm I set it at. I disconnected the O2 sensor when I went to lunch to see if that improved the idle, it didn't so I reconnected it. Then when I drove it home last night it threw a check engine light with code 17(feedback system). I popped the hood and made sure the O2 sensor was fully connected, it was and read the code. I have not had time for any further troubleshooting yet. Any ideas on what the most likely problem is?

 

RX7 FD and Series 5 Error Codes

 

Had a chance to dig a little deeper yesterday towards the end of work. Pulled my spark plugs out, they were fouled black with carbon. Cleaned and reinstalled all 4 spark plugs. Checked codes again, this time it had codes 12 and 18 as well for throttle position sensor. I disconnected it and inspected the terminals, they had some corrosion. I cleaned the terminals with contact cleaner, applied dielectric grease, and reconnected. I cleared my codes then I drove home. Car ran much much better at first but by the time I was almost home it was starting to run poorly again and throwing code 17 again. The code came back before it started running poorly though. Seems like it's running way too rich and/or has incomplete combustion causing code 17 and fouling my plugs causing the poor idle, power drops, and misfires.