I have a 98 Navigator with a 5.4
I'm having problems with idle and running issues 1. Starts and stays in a high idle around 1-1.5 rpms then in gear drops to only come back up staying above 1000
When driving seems to miss but I just changed all coil packs
2. Sometimes it'll idle down to normal but still drives like it's loaded up
I've changed iac,tps bad pcv boot behind intake changed plugs and intake gasket still with all this it's still running awful
Oh sometimes after running I'll shut off and will have to hold pedal to floor just to start
Need help thanks for reading!!!

 

If all simple maintenance has been looked at, -

Look at the EGR valve, - you can suck test it or just by-pass it temporarily by blocking it off completely. I'd block it completely to confirm the valve isn't hanging open.

Once that's done, check the converters for blockage or excessive heat.

The fact that it's missing, having to hold the pedal down for start and that it actually stalled leads me to believe it's the EGR valve stuck or hanging open. But, when the engine is acting up in this way the procedure is always fuel first. Check delivery/pressure. Other than that, those old 4 valves can be a mother to keep running right lol.

Just block the EGR port, - slide a piece metal or whatnot between the EGR valve and TB elbow. Tighten it back down to pinch it, fire it up and take it for a drive. If it runs 100% better....