Help on a 350 Turbo w/CAT - Idle surge on startup

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Hi, first post here. History:  Son (welder) purchased used 350 PipePro w/1.5 T CAT.  Previous owner indicated governor control module would need replacing, they had bypassed ACT+ and ACT- (J1 Plug pins 5 & 8 respectively) with a toggle switch.  This forced the engine into a constant high idle and was able to weld.  Took apart the old faulty module, and sure enough the board was burnt at the approximate location of act+ and act-.  Assuming rest of board was unaffected since remaining wires of plugs still plugged in and nothing else wrong observed with engine or welder at the time.  Not wanting to keep a non-standard configuration in place, we replaced with new governor, patched/spliced/crimped two wires back to the J1 plug (removed from toggle switch).  Hence, removing the toggle switch.  Observing the labeling of the +/- wires mentioned, they go to the linear actuator  (ACT) or throttle solenoid (one and the same?).  Problem:  Since replacing with new governor and undoing previous "hack" or toggle switch workaround, upon initial startup the idle surges high to low.....repeatedly.  My understanding from discussing with my son is at some point it should step down to the lower rpm after startup and idle there until welding commences.  But you should never get surging, especially after startup.Attempted solutions:  CAT mechanic says engine is fine.  Welder side mechanic says couldn't find anything.  Not sure if either really spent a lot of time diagnosing, since each one had the welder for weeks at a time and problems still exists without any progress or direction.  Miller support has been helpful with suggestions so far.  Recent suggestion was to clean and reset MAG speed pickup.  Decided to replace entirely.  Not knowing required depth to flywheel, bottomed it out and backed out approximately 3/4 turn.  May have improved slightly with high idle immediately after startup, but then surging persists as it has always been. Question out to Miller if maybe it needs another 1/2 or 1/4 inward before I touch it again.  I'd like to actually swap out the ACT+ and ACT- wires to the plug because of possible fraying or whatever might affect them.  The pins in the plug look fine, not melted or burnt that I can see.  But since wires were spliced perhaps leading to some inconsistent current, if that's possible.  I've used a multimeter (not an expert) but I get tone or continuity from actuator down to plug for the two pins in question.  Not sure if that's enough to say it's acceptable, or inconsistencies could still occur after startup.We doubt it's fuel or motor related.  Unless there's something else up with this machine we're unaware of, it did work initially at a forced high idle and weld, but after backing all that out and installing a new governor and splicing wires back together, we feel it should be working properly today.  We're hesitant to throw more parts at it or blame some other non-electrical piece for this surge issue.Ideas, direction, or solutions?Thanks in advance.Miller Big Blue 350 PipePro TurboCAT 1.5 T
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