whats causing the p0306 code on 1997 GMC Yukon

replaced rotor cap plugs wires o2sensors mass airflow sensor and still getting code p0306 and it has a distributor and a throttle body, so what now

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2 answers 1 comment
Did you clear the code after repair? If so check compression and for a vacuum leak on or near # 6 cyl. Third cyl on pass. side.
check the coil
Only one coil for all cylinders. Should not set po306.