2009 Aveo5 intermittent acceleration problems in heavy rain

My 2009 Aveo5 LS manual transmission recently started having intermittent acceleration issues in rain. This issue doesn't always occur when it's raining but I notice that when it does occur that it's in heavy rain.

When driving at highway speeds in 5th gear in heavy rain the rpms will drop for about 4-5 seconds even though the accelerator is pressed to the floor (as if the TPS was unplugged), and after the 4-5 seconds power is restored again. During those 4-5 seconds, pressing the accelerator doesn't stop the rpms from dropping, but if I press in the clutch I can rev up the rpms . This "on and off" cycle of having no power for 4-5 seconds and then having power again for 4-5 seconds usually happens for 4 to 5 cycles before everything operates like normal again.

I've only noticed this cycle of power/no power occur once per trip, so I may continue driving for another 15 or 30 minutes and it doesn't occur again during the rest of that trip. This doesn't occur in light rains or in any gear lower than 5th, but only at highway speeds in 5th gear in heavy wet rainy weather. No CELs have ever triggered at all, so when I took the car to a mechanic to have it checked out they didn't know where to start to troubleshoot the issue and weren't able to recreate the issue since it doesn't always occur.

Has anyone had anything similar happen that they were able to successfully resolve, or does anyone have any idea of what may be causing this?

TIA!

When you run out of possible culprits, i suggest taking a good hard look at the wiring harness to chassis ground connection right beside the ECM in the engine compartment. If the ground connection gets corroded, it can cause a wide variety of driveability problems. When i tried to unbolt that connection on my 2009 Aveo to clean it up, it was so corroded that it snapped off. Be prepared for the bolt snapping off, or else be prepared to use an alternate nearby location for bolting down the wiring harness ground connection after you clean it up. Deano

Deano, interesting that the other day I read a post from you in 2020 (I think). I am going to have my mechanic check the ground wire near the ECM from the harness. I live west of you in Milton. I have read other posts from Canadians who have weird problems with their Aveos. Perhaps salt related mist? I had new gas pedal put on last year which eventually went back to rpm's bouncing up and down, sometimes going into limp mode. New throttle body recently and the other day it started acting up like the old one. It stalled twice the other day, I just started it and let the rpm's bounce around without touching the gas and it stalled (never did that before). Seems when I start it and have light pressure on the gas and gradually increase and temperature rises a little it will run fine,(may have a little rumble starting down the street) but I ease off the pedal a bit and it's fine. Will post the results after the mechanic puts new rad hoses on. Thank you for your suggestion.