Took the car out in May and had the following problems: car missed in some corners. Real rough at idle when the engine cycles down from 1200 rpm to 900. Just started to work on the car last week and here is what I have done. New plugs and wires. Changed air box out with our other car that is working fine. Checked fuel pump flow as per Mike instructions, very good result! cleaned lifters. Replaced pcv. Replaced fuel filters. changed computer and edis. Changed green and brown relays.

Checked the engine codes test while not running. Had the following code:113 intake air charge temp above max voltage. Fixed this problem by changing the air temp connector to box.

Engine codes while running. 172 02 sensor fault/lean , 411 can't control rpm at low rpm check
412 Can't control rpm at high rpm check, 538 insufficient rpm change during response test. I know that A/F is all over the place when the car is not on the track, but compared both of our cars at idle and at 4000 rpm. Much higher readings on the car that I am having problems with. Not sure that means anything.

Replaced o2 sensor. replaced o2 connector. replaced pcv valve, replaced all vacuum hoses. Codes still there.

Car ran well last year. The only thing I did over the winter was take out the fuel cell and checked box etc. Could this be source of problem. Sounds electrical to me.

Pat, I'd swap fuel rails/injectors and check the two cars' a/f ratios.

Fuel pressure?

My bet is with RacerX, clogged injectors...

Injectors don't know if you're in a corner but the fuel pickup line does. You've been in the fuel cell ... I'd start there. The codes are misleading.

Also look at the wires on the crank sensor. With engine torque (in a corner) they move and there may be an issue there.

I agree with Rex, Take the time to double check cell, but if car ran poorly before you did this then move on. You said you replace air box with one that you knew was good. Then you said you had to change air temp sensor. So how good was it really? You did change mass air flow sensor with box. If yes and it still idles rough move on. Since you have another car you can keep going coil etc. also you can not hear any vaccum leaks? spray carb cleaner all around intake to see if idle changes. Wire test. As I call it the wiggle test. Grab wires and wiggle see if you can hear a change. Pay close att. to wires behind alternator and grounds on engine blocks. But the rough idle leads me to think it is a sensor issue. You can also pull injector wire one at a time to see if it changes idle which it should. I will think some more wife is calling me to dinner.