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This can be caused by a number of things including a faulty distributor a faulty crankshaft position sensor a loose reluctor wheel and sometimes clogged catalytic converters Remove the Crankshaft Position sensor and check the reluctor for being loose or cracked. Try shimming the Crankshaft Position Sensor per TSB #02-06-04-059. Test exhaust back pressure. It should be less than 1 PSI at 2000 RPM in park
Yes the sensor is set at the factory but because of the normal wear it can need reshimming,
if you remove the upstream oxygen sensors then you can use a gauge attached to the open port to read the presure