1996 Ford Probe Engine missfire

The car has very low power and when you accelerate it backfires into the intake. I have replace the distributor and timed it to ten degrees btdc. I have checked the camshaft timing and it is correct. If I restrict the air flow to the intake the engine smooths out and starts to run better. Could it possibly be a failed egr valve or a failed VAF feeding the ecm false data. I have also replaced the crankshaft position sensor