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engine on 1998 Nissan Frontier

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
v6 engine runs perfect for 30 miles then starts ,run eractic or pulsating ,like turning switch on and off. has 135,999 miles
(1) Answer
could be fuel pressure or spark. you need a shop to look around in the computer for freeze frame data to see what has failed.

Roy