87 chevy pickup

when i got my 87 chevy pickup it had a 305 in it and i decided to put a vortec 350 in it. Which i had to get a conversion manifold from GM so i could put the throttle body on. but for some reason it will start shaking around 1200-1400 rpm, kinda like a miss. when its cold and in open loop it as a erratic idle. Its running really rich and bad fuel mileage, i took it to two shops and said the manifold was leaking and told me to put silicone on the intake gaskets and now i can spray B-12 or brake cleaner and i cant find a leak.

Everything is replaced like Engine, Throttle body, distributor, ecm, map sensor, tps sensor, iac sensor, egr.

Also at highway speed it will turn the check engine light on but for some reason i cant read the codes. When i plug the code reader in it says that its basically not connecting.

Give me a direction please. Im clueless

when i got my 87 chevy pickup it had a 305 in it and i decided to put a vortec 350 in it. Which i had to get a conversion manifold from GM so i could put the throttle body on. but for some reason it will start shaking around 1200-1400 rpm, kinda like a miss. when its cold and in open loop it as a erratic idle. Its running really rich and bad fuel mileage, i took it to two shops and said the manifold was leaking and told me to put silicone on the intake gaskets and now i can spray B-12 or brake cleaner and i cant find a leak.

Everything is replaced like Engine, Throttle body, distributor, ecm, map sensor, tps sensor, iac sensor, egr.

Also at highway speed it will turn the check engine light on but for some reason i cant read the codes. When i plug the code reader in it says that its basically not connecting.

Give me a direction please. Im clueless

Jumper pin A & B on diagnostic connector and read codes from check engine light.
Post back code.
All sensors pluged in and woking right?
Make sure map sensor is getting proper vacumn.
And tempt sensor is working.
And both reading right to PCM.