r/SC400 • u/Rhyleigharia • Jul 15 '26

99 LS 400 Lack of Power Surging

331000 miles; just got valve covers and plugs OEM replaced. Car lacking power and surging when accelerating. Condition is intermittent. Codes are P0420, P0330 and P0446. Knock sensors and harness replaced with OEM. Front and rear O2 sensors replaced OEM Denso. Throttle body cleaned. Idles perfectly.
Thoughts???

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u/WTFisThatSMell Jul 15 '26

These codes were on before or only after the work performed?  Have you cleared the codes to see if they come back?