I have an 89 geo metro with no egr valve. I put a pressure gauge on it, and at idle it reads 0 Hg. When I give it some gas it'll go up to 10Hg then drop to zero, but if I get it up to 15Hg and hold the accelerator the pressure hold, but instantly drops to zero when I let off. I can't find a leak anywhere though.

it's leaking somewhere, do this video to find it https://www.youtube.com/watch?v=zMok2y05jNE