Start with basics....
Take plugs out what do they look like. oil or gas fouled. are the worn, replace them is so. Check ignition wires, are they in good shape, are they connected correctly?
check fuel pressure. check if vacuum irmc is actuated when engine started. When engine starts it should pull vacuum and close secondaries. If not check for vacuum line leaks and /or replace irmc valve.
Do you have a cell light on? Purchase a 50 dollar tester and run a koeo test. See what codes are pulled. I recommend you do this before tearing into the engine. Once you start breaking it down you can't run anymore tests until it is back together and you may be back at square one.
If you have dtc codes what are they? Do a compression check on engine, what do you get?
Bob
