Hello, all!
Recently I had to replace the starter and radiator in my shop's Mitsubishi forklift. After the repair was complete I drove it around the shop to see how it did and it seemed to be a little more touchy with the throttle than it was before. I paid it no mind. After complaints from fellow coworkers about the throttle randomly surging and having them nearly run into things I looked at it further. What seems to happen is when the hydraulic system gets put under high load such as the wheels being at full lock or any of the fork controls meeting it's max (tilt being all the way back, side shift being at it's full max) the idle will drop, vacuum will then spike up and make the throttle surge up. I have checked for vacuum leaks, checked the coolant temp sensor, cleaned the throttle body with carb cleaner, adjusted idle settings and still no change in behavior. I'm not very familiar with this specific propane injection system or it's parts so any help would be great.

Make: Mitsubishi
Model: FG40K
Serial: AF 876-0317
Engine: Chevrolet vortec 4.3lt v6