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The first thing you need to do is scan the ECM for faults. You can get this done for FREE at any Autozone and a lot of other large chain parts stores.
I would suspect that it may be your Mass Air Flow sensor (MAF) but I hate to just throw expensive parts when you can get the faults read and pretty much know for sure what the issue is.
When you have the fault codes, post them here and we can diagnose it accurately.