kilimantastic

My brother and I are working on his 93 Pickup, thing ran great when I had it. My brother the new owner, did a coolant flush, and whilst we were flushing the engine revved real high then just stopped. We couldn't figure out what was wrong with it so we just let it sit and dry out. Ran great after that for a while that is. So, we thought it must've been something else, below is a list of all we checked and did so far.
it is a 4 cylinder Automatic.

Mutlimeter was used to check-
MAF
Coolant Temperature Sensor (also dunked in hot water for proper testing)

Replaced in order-
Spark Plug Cables
Fuel Filter
Exhaust Manifold Gasket.
Sending Unit

List will be updated as things come to mind/are worked on.

This is the kicker! After applying pressure at the top of the engine (on the efi)
the idle runs great! No problems at all, it starts rough and requires a bit of gas at the peddle but when I apply just the slightest amount of pressure at the top the engine's idle runs great!
Could this be a problem with the fuel system or the intake manifold? I'm very curious and need to get this running soon, it's a daily driver and a work vehicle.
Inquire as much info as you need below thanks in advance!