The 4G54 isn't the simplest engine to work on even though it's 'only' a single cam 4 cylinder. To do anything on it requires tearing almost 1/3 of the engine apart, the stock carb is the stuff of nightmares and there is always some confusion over timing and starter motor compatibility etc. Most shops don't have a clue about them and invariably mess something up. That being said, the steep learning curve is worth it. When you get it glued back together with the new carb, it'll be a whole new beast to drive.