Well, it sounds like you basically have a rough idle going on, and a lot of the time, that can be something simple. Normally, if you dont have any horrible noises occuring, that narrows it down to either fuel, air, or vacuum, and it being a 1999, I'd put my money on it being a vacuum leak. However, you can check your air filter and try running some "Sea-Foam" and run a higher grade (and non - ethanol) of fuel.
If it does end up being a vacuum leak, its probably best to bring it too a mechanic simply because its fro 1999 and there is just about a billion vacuum lines. But if you are careful you can grab a can of starter fluid and try spraying it sparingly onto vacuum lines while the truck is running, if it suddenly idles different while you are spraying one of the lines, that normally tells you thats one of the vacuum lines giving you trouble.
Hope it helps!
All around mechanical, Old-school mechanic
· 7 years ago