Been trying to track down the cause of this on my '88 Pioneer 4.0, 5 speed. There's a random popping in the intake while idling, and will make a nice loud pop when hitting the throttle. I replaced the vacuum harness and changed spark plugs and wires. I'm going to check the timing next, probably should check the fuel pressure, going to seafoam everything, make sure the Distributor is clean and not warped, make sure the wires are hooked in the right sequence, then start cleaning/replacing sensors. I've been just doing research trying to narrow down what can cause this. if none of these work, at least I'll have cleaned up some stuff in the engine bay.
If anybody has any other suggestions I'm all ears and will give any advice a shot. You can here some more engine noise in the video, I'll be trying to find the cause of that too.
Also.. there's a connection coming off the harness around the intake and vacuum lines that is not connected, and I havn't been able to find a place to plug it in for the life of me. I'm thinking it has to be a sensor that just is on automatic transmissions, mines a 5 speed