Q: It misses at idle and on acceleration. More so under load. on 2003 Mazda B2300

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My wife just got a 2003 Mazda B2300 from her dad with 62000 miles on it. It ran great for about 650 miles, then it started missing at idle and when pulling a hill. Taking it out of overdrive doesn't help. Most of the time it will miss when at full throttle. A time or two it didn't. Also we ran a bottle of gas treatment through it. It didn't help. Does a bad coil pack cause these symptoms? Any suggestions would be appreciated.
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Suggest pulling plugs to start. keep track of which cylinder each plug came out of.have some one who is knowledgable about 'reading' plugs take a look for signs of poor wear or firing. MAKE SURE that you have the factory specified plugs in it!!! sometimes aftermarket will sell you fancier plugs OR the incorrect cheaper plugs. check for signs of restricted exhaust.if suspected , improvise by 'creating a leak in front of the 'restriction' (loosen something...carefully) and test driv or monitor with vacuum guage or scanner (MAP or BAP voltage)