LX93conv

my 93 has some new problems..check engine is on and off maybe a day or two before it comes back on..ran a code check O2s run lean..check the code a day later no O2 codes show up car sometimes has no power and some days it runs great gas mileage is very bad at this time..seems like the timming is changing just by the way the car sounds ..car is at 12 degs total motor is stock just the normal bolt ons.. headers cold air Mac high flow cats...flow masters
any help??