I have 1999 Mazda pickup 3000, auto, 6cyl., ran good, but wanted some fresh plugs. Replaced the spark plugs and new wires. Now runs poorly. Low idle shake and slight back fire upon acceleration. I tried searching this forum, but went down a rabbit hole. Is this a simple timing fix or ?

 

Going to guess you have a couple spark plug wires crossed on the coil, usually on the drivers side.