First, you should check to see if you didn't put your mass air flow sensor in backwards, the opening should be facing the filter. After you checked that, I would listen for hissing or vacuum leaks. If you have done a intake manifold swap, there could be a leak somewhere around it causing it to have unmetered air coming into the engine. Also, check under the throttle body where the coupler is to make sure you don't have a gap from the rubber coupler to the throttle body. Make sure you pushed your pcv connectors on tight, the one after the throttle body can be a little hard to snap on sometimes. Hope you find your problem.
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