Welcome to Club Frontieir.... Sorry to hear about your misfire in Park only. Appreciate if you could give us a little bit more information so as to help you diagnose your issue. Are you the original owner, (bought the truck new off the lot), or 2nd / 3rd owner? What motor do you have in the Frontier? The 4 cylinder QR25DE motor or the 6 cylinder VQ40DE? How many miles do you have on the motor? Do you know the maintenance history on the truck / motor? Do you know if the cam shaft & crank angle sensors are the original ones on the motor or have they been replaced? Did you use Nissan OEM spark plugs & coil packs or aftermarket ones?
If you're not aware, the 2nd Generation Frontier motors are a bit more finicky when it comes to servicing the engines. They don't tend to like aftermarket parts - use the SEARCH function at the top of the page & you'll find several posting from Club Frontier members having issues with aftermarket parts. People seem to have better luck using NGK or Denso parts as Nissan tends to use them as OEM parts.
You might want to start your misfire diagnostic by plugging in your OBD-II Code Reader, (hopefully it has Live Stream Data capabilities), & check your Short Term & Long Term Fuel Trims. If your fuel trims are within specification and your oxygen sensors are working fine, then you don't really have to worry about having any vacuum leaks which can cause a misfire. Do a visual inspection of the accordian-style rubber boot that leads to the Mass Airflow Sensor - that rubber boot tends to get small tears in it as it ages - your truck has 17-18 years on it. Check all the other vacuum lines while you are at it too. Use some carb cleaner to spray around the fuel injector o-rings just to make sure those are fine also - they tend to get brittle with engine heat & age too.
You might want to download a free copy of the Nissan Factory Service Manual from any one of the attached three weblinks listed below. YOu'll need it to help you troubleshoot & diagnose the issue causing your misfire while in Park. Hope this helps...Let us know if you find anything or have any additional questions. Good Luck!!
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