Does not start after project

[Bmw E30 Finalnd]

I have a e30 320i 1990 project build and i havent done any changes to the engine other than changed the exhaust manifold and now it dosent want to start good and when it’s started it dosent want to hold on idle. What can be the problem? I have taken the intake manifold off for painted but i’ ve put it back correctly. Can there be any air leaks or is it something wrong with the fuel system?

[95BMWIC]

Broad question - could be anything - may not be related with the work you did at all- or it could be.

Check all electrical connections and then make sure you have no vacuum leaks (sounds like a vacuum leak).

Was the intake manifold gasket new?

[Bmw E30 Finalnd]

Yes i’ve changed the intake gasket but i should check if there’s any leaks and if all the connections is conected