Fluctuating RPMS

[RIGGNTS]

I have a 1998 5.0 GI PBYCCE. Just repowered, break in is done and been fishing some. Now the RPMs fluctuate about 1 to 2 rpms (without touching the throttle). Seems to happen at all rpms. Throttle Position Sensor?? Any tips on this one?
I did look at a ton of post and did not see this specific problem.

 

[Saline Marina]

I'm going to ask for clarification here. Is it really 1-2rpms or a complete loping run with 1000-2000 rpms (which might be 1-2 Large Graduations on the dial). I'll ask if it did this from the day the repower was completed or its an issue which suddenly cropped up. Also, is it the gage only fluctuating when the engine has a steady audible note?

 

[RIGGNTS]

Good questions...
It is only 1-2 RPMs. For example, if Im cruising at 3200rpms it will fluctuate between 3000 and 3200 on the dial. And yes I can hear the difference in the engine when its happening. Definitely not just the guage.
It did not do this during break in cruising that I can remember. 2nd from last trip was offshore and I noticed it some. The last trip I noticed it the entire time. Even when idling out of the creek it was surging and dropping back, and when I planed out it did it too,

 

[Bondo]

Good questions...
It is only 1-2 RPMs. For example, if Im cruising at 3200rpms it will fluctuate between 3000 and 3200 on the dial. And yes I can hear the difference in the engine when its happening. Definitely not just the guage.
It did not do this during break in cruising that I can remember. 2nd from last trip was offshore and I noticed it some. The last trip I noticed it the entire time. Even when idling out of the creek it was surging and dropping back, and when I planed out it did it too,

Ayuh,.... Welcome Aboard,...... Can't help ya with any 'puter sensor problems, but try changin' yer fuel filter, 'n inspect the contents of the take-off for water,.....

 

[Saline Marina]

Not totally sure on the magic bullet here. The TBI motors seem to have higher than average problems with the fuel pumps, from what I read in other posts. If it were me, I think I'd try to renew those due to the age if they are original, sort of an insurance policy against breakdowns even if that doesn't fix the issue. The vacuum leak doesn't seem to be the right answer because it would probably die at idle. I might also inspect the wiring harness in case there's something like a cut somewhere that's pulling the ECM voltage down (but not enough to blow a fuse) and clean the harness grounds. Last strange idea would be a bad voltage regulator which is allowing a sag/surge in the output voltage of the alternator that's then causing fuel pumps to spin faster and slower. The battery should provide some damping to any slight AC ripple in the alternator output but if it were a large enough problem maybe the battery can't keep up. Its hard to diagnose over the internet but at least I can give a few things to try & eliminate