I had an Isuzu Trooper with an early multiport EFI setup on a 2.6 4ZE1 engine. It basically ran on controlled vacuum leaks. The easiest way anyone ever found to fix it was to remove it and swap in a carb setup from a 2.3 4ZD1 engine. I decided that when coping with a 1980's Isuzu the most effective way to solve all your problems was the radiator cap solution: Remove the radiator cap and hold it up, then drive another vehicle under it. Put the cap back on and it will run better.