And yes I put in all new ngk spark plugs three weeks ago.

 

Did the car work fine at one time, with these modifications?

 

Yes it's been 3 years if not more with the same mods.

 

I would compression/leak down.

 

Those codes have to do with the mss airflow sensor. When the cat is plugged the air flow is all wrong. You will get a standing air wave that acts like a valve that open and closes erratically causing major drivability issues. Try pulling out the front oxygen sensor. That will reduce the back pressure in the exhaust system enough not see if that changes the nature of the problem. It's free , just maybe some skinned knuckles.

 

Does the S2000 have a MAF? I thought everything was controlled via the MAP sensor.

 

Duh... you are correct Disregard that comment as I apparently was not thinking there I have 4 cars, 3 of which have MAF sensors!

So to bring it back to the RIGHT vehicle, I should say to address the rich running condition first as that is where the codes start showing up. P0172 and P0170 are both popping up for him per this and his first thread about his issues.