98' f150 V6 4.2
Just bought this truck a few months ago and it started running pretty rough so i changed the plugs and wires. Rpms are now fluctuating between 500 and 2000 when idling. I triple checked the firing order, properly tightened and lubricated the plugs, set the gaps at .052" and made sure all of the connections were solid. I am 100% certain I did everything right but I don't know how to troubleshoot this rpm problem

 

First, check for any codes. Some may be pending and haven't tripped the CEL yet.

Possible causes are outlined here.
https://axlewise.com/rough-idle-meaning/

 

yeah I was having this issue but rpm’s we’re also fluctuating as I was driving. There was no CEL. I was 200 miles from home but made it. The CEL finally came on about 40 miles from home. In my case it was an 02 sensor code that was easily fixed in my driveway. I was surprised how long it took to trigger the CEL.

 

I don't know if this is your problem but if you just bought the truck, the mass air flow sensor is an often overlooked maintenance issue. You should clean it using mass air flow sensor cleaner available at the big box parts stores. When it is dirty, your engine doesn't get the proper air/fuel mixture and the truck doesn't run will. This is located just back from your air cleaner. and an easy job to accomplish. It was surprised at how much better my truck ran after I cleaned mine.