I have a 90 f150 with a 5.0 it runs a drives fine unless I drive it for 45+ mins then it wants to idle rough and die. Any ideas on what this could be?

 

I would check for vacuum leaks since it's fine as you are driving.

 

But it's fine every other time just when I start slowing down after about 45+ drive time

 

It could be the TFI module on the distributor heat soaking. I have the same model and similar issues. I would get a new one and buy the relocation kit they sell for mustangs. It moves it away from the engine heat. Solved my problem!

 

I found the issue the egr messed up or something and when I unplugged the vacuum line on the top it started to idle fine. I don't know if this causes any other issues but as of now it runs and idles fine.

 

You plug the vacuum line?

 

Yes but the little bit I didn't have it plugged i didn't find any issues.