I have a 5FGC25 Toyota forklift that stalls everytime you let off the accelerator pedal. Runs great as long as you are Accelerating. It has been converted to a 12v Lock off on the regulator. I replaced the Regulator but still have the same issue. Have no service manual for that model. This is our oldest forklift that we use in Maintenance. We have 8 Series for our production. Any ideas on what to try please let me know