2002 Isuzu Axiom Check Engine Light Trouble

Here's what's already been done: Spark plugs replaced with NGK platinum, engine tuned up, flex tube put on exhaust to fix leak. Then to another mechanic who had a better tester, and manifold intake gasket replaced because it was leaking. Fuel pressure checked and okay. Don't feel any missing, and the vehicle runs fine. No codes showing. Still need to check tune up? Second mechanic doesn't think it's the plugs. I love this car/truck, I want it fixed.

Okay, more info since you seem to be puzzled, as does the other mechanic on JustAnswer. Com: 2002 Isuzu Axiom Check Engine light. Stays steady on startup, steady on less than 2000 rpms, flashes when accelerating above 2000 rpms, goes on steady when not accelerating or when braking. Engine runs fine. Had a missing problem, replaced the plugs with NGK platinum, replace fuel filter and flex tube on exhaust. Still flashing. Took to another mechanic. He replaced manifold intake gasket, checked fuel pressure and put back on tester. No codes showing up. He can't figure out what the problem is. I'm a woman. This is making me nuts, although from what I've read this seems to be a common problem with this vehicle. I bought it "preowned" last October, and CarFax was cleaner than a whistle. Humans made this dang thing. A human should be able to fix it. Any other ideas?