I check compression 120 on 3 cylinder. Won't pass smog

Check engine light on they can't they can't pass it check engine has to be off

Trouble code PO303 present when scan tested? .. Check engine light flashing while driving?? .. Can you answer those questions???

Scam show po303 when tested check engine light goes off and on but once I get on road in 30 to 40 minutes the check engine light goes off they come on next day