HiHere is an update and a recap.
Sudden problem of popping under load.
Replaced plugs, wires, cap/rotor,and idol air control valve . Problem persisted, but maybe slightly less so.
Checked compression. Looked good. Mechanic said it was running rich from looking at all plugs and recommended replacing MAP sensor and coolant sensor. I replaced only the MAP sensor along with a different set of plugs (NGK V-Power 3951) their site matched them to my VP5.7GXI)
Engine idles smoother and no popping/backfiring under load at all or any time. Idle is slightly rough when cold. Idle fluctuates up and down from 650-1000, more so when colder. I suspect it still is running rich. Exhaust smells of gas more than normal. New plugs look black and oily/fuel covered looking.
I replaced coolant temp sensor and fluctuating idle improved did not get to take it out on the open water). Went back today to pull out for the season and cold idle is slightly rough and idle RPM still fluctuating, not noticeable when cold, but more after it warms up.
I plan to get a mechanic to look over the winter/early spring and check what I can when it is in storage (indoor/heated)
Thanks for all your help with this. If anyone has any ideas, please post.
I thought it would be iridium NGK 5599/5999 plugs for that. It is for all the mpi same engines.