I have a newish 725 hp NA BBC with a mefi 4 computer. When you put it in gear and want to plane out it will go lean and start back firing through the intake. Out of gear it idles fine. It's always done this since I got the boat back. After about 10 min it will clear up somewhat and you can get on plane. The rest of the map runs like a top. The tuner had us increase fuel psi but the problem stayed and all we did was foul plugs. We ended up putting in a gauge and we put it back to the builder/tuner advised psi

One trip while troubleshooting we unplugged the tps sensor and the problem fixed itself. We sent the ecu back (i think the 4th time we did this)to the builder/tuner and he said the idle control file was corrupted. He reloaded it and sent it back with a new tps. We put it back together and the problem is still present.

At this point all i can think of is the wiring harness is bad(or maybe is picking up RF noise) or the ecu is bad. I would think if it was a wiring issue it would not be problematic in just one spot if the tune.

Any thoughts/ideas would be welcome

Sounds like you need a new tuner, could be warm up enrichment, acceleration enrichment, to small of numbers in the base fuel map, wrong A/F ratios for that temperature. Articfriend may have an idea.

IF the binary code in idle file became corrupted/ jumbled and caused this issue, I would have your tuner look at it again and see IF it did same thing. I tuned a mefi1 once that did similar, have your tuner flash a spare ecm and see what that does.