Suddenly running like crap, where to start.

[Leviticus]

Hey guys,

Been a while, been busy with work and have been ignoring my truck. So I fired her up the other night and she was running great like usual and took her for a spin. She was great until I pulled in the driveway and was getting ready to shut her down and gave it a little rev and all of a sudden the idle drops to 500 from 850-900 in park with a rough idle and shaking all over the place.

Now it will start but doesn't want to stay running when cold and gives little pops in the exhaust when giving it a little gas.

Haven't had much time to dive in deep, but checked the timing and it was a little off what I had set it at so re-set it and though I had it... nope. pulled the fuel filter and bypassed it, and seem to be getting spark at all cylinders.

What I did notice is that when I pull the air filter and either choke it 80-90% or cover the intake with my hands the idle comes up and it runs smooth. Maybe too much or too little fuel? Or a leak somewhere in the intake manifold? What would cause that?

Putting a mini starter in tomorrow, and fixing this issue. Where wold you guys start? Also it has an electric fuel pump and I haven't had a chance to check fuel pressure.