2.9L Doesn't start

[Brumby]

I have an '86 A4LD and Prior to this it had a hard time idling in park or neutral, but it would start right up cold then after 10 seconds started to struggle and would die if i didn't give it gas, i recently put a new 2.9 in and put the old exhaust manifold on the new one and after that it just wouldn't start, it'll turn but won't start, it sounds like it wants to and comes close but it doesn't. I have no idea whats happening any tips? This is my first car so I could use all the help i can get.
I have already checked for spark, checked wires, gone through most of the stuff in the service manual (which sucks)