engine wants to be run at 30 BTDC...?

If some of you have been following my posts on here, you may know I've recently rebuilt my stock engine in my '94 mercury villager. When I first put it back together and slapped the distributor on, I thought the computer controlled all of the timing, so I just put the distributor on close to the right spot and fired it up expecting the computer to sort it out with the cam sensors and what not. It ran 'alright', I guess, but had horrible power - seriously pathetic. Then, I advanced the timing a bit and it significantly improved. I read the book on the proper way to time it (15BTDC) and did so, but it still wasn't running right. I carefully kept advancing it a bit and it seems as though the engine is way happier and smoother at 30BTDC. I'm too scared to push it further than that. Anyone know what's up with the crazy advanced timing? I was super careful to get the timing belt on properly when I put it together, but I guess it's not out of the question that I may have missed a tooth. I've also heard theories about EGR stuff affecting timing. Could this be possible as well?

it's possible you ar testing the wrong plug wire, or firing a diferent plug.

check the other plug wires